# My horse trailer lights sometimes don't work? Ideas?



## beau159 (Oct 4, 2010)

My trailer has been in the shop 3 different times (one was at a different place) and no one can seem to figure this out. It's also happened with two different pickups so it can't be the pickup. 

I have a 2003 Exiss gooseneck trailer, with a dressing room in front and 3 horse slant in back. There is a light switch for a flood light and my dressing room lights, and then there is a light switch for the flood light in the back and the inside of the horse's area. 

Sometimes, I have my trailer unhooked from the pickup. For example, this weekend I was at a large barrel race where I unhooked the trailer so my horse's could stay in their electric fence and I could drive the pickup to my hotel room (my dressing room is NOT living quarters). But I had to run my second horse after it was dark out, so I simply plugged the 7-way cord into the pickup so I can still use my flood lights to see what I am doing. 

Worked fine while I saddled him up. Turned off my light switches and did my run. I did not touch the 7-way cord. 

Came back and my horse trailer lights won't turn on. I even turned on the pickup (thinking I somehow had drained the battery or blown a fuse) and _nothing_ would light up. My pickup (2014 GMC) also said "check trailer wiring" on the display. 

This has happened before; where sometimes my lights will work (if the trailer itself is not actually hooked up to the gooseneck ball) and sometimes they won't. I can understand that if the lighting is not grounded properly, the lights won't work. 

But why does it sometimes work, and sometimes not?


Maybe a mechanic can clue me in.


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## disastercupcake (Nov 24, 2012)

Check the connection the bulbs!

This happens to my trailer every year. I live on a dirt road. You just have to wipe the dirt off of the connection to the lights. Especially if your lights don't have a fully enclosed housing. 

All you need is a screwdriver to take the cover off, and a pencil eraser to rub the dirt out until the metal is shiny. Easy, but dumb, and you will probably need to do it every year.


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## blueriver (Oct 10, 2009)

Ground ... alot of times they ground better when hooked to the ball ... I carry a special ground wire that I plug into the ground on the 7 way ... the other end has an alligator clip that I ground to the bumper (when I'm not hooked up)


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## Mingiz (Jan 29, 2009)

Could also be a loose wire or pin in the plug it self. :wink:


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## Chevaux (Jun 27, 2012)

Worse yet - it could be all of those things the other posters mentioned going on at once and good luck sorting that out. Btw, I have light problems with my old trailer also - my solution for that situation was to buy a new trailer.:lol:


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## stevenson (Sep 12, 2011)

could be a mouse chewed a wire, so it shorts out. DH is having to rewire our trailer completely as the lovely ground squirrels or rabbits chewed all the wires..


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## beau159 (Oct 4, 2010)

Let me add that when the trailer is completely hooked up to the pickup, I've never had a problem with the lights. 

It's just when I need to unhook the pickup ... but still have my flood lights and dressing room lights turn on.

*BLUERIVER* - can you post a picture or a link of what you are talking about? That sounds like what I need!


My plugs and adapters can't be the problem. The 7-way on the trailer has been redone twice now (once just this spring), and the adapter on my hubby's pickup (that I was using last year) had a brand new one put on last summer, and the new pickup I'm using now the adapter is barely a month old. I've had the darned things "fixed" so many times, they better not be the problem!! haha.


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## stevenson (Sep 12, 2011)

so it runs off a battery when not hooked to the truck ? faulty battery ?


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## beau159 (Oct 4, 2010)

Maybe I'm not explaining things clearly. 

When I have the gooseneck ball attached to the pickup, and the 7-way plugged into the outlet on the pickup, it all works fine. 

But if the trailer is just sitting there and I try to ONLY plug the 7-way into the outlet on the pickup, it sometimes works and sometimes doesn't, for me to turn on the flood lights and dressing room lights on my trailer. 

So it runs off the pickup battery. Of course, the pickup does not need to be on for the trailer to get power.


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## Chevaux (Jun 27, 2012)

beau159 said:


> ...
> But if the trailer is just sitting there and I try to ONLY plug the 7-way into the outlet on the pickup, it sometimes works and sometimes doesn't, for me to turn on the flood lights and dressing room lights on my trailer.
> ..


I was serious in my other post about multiple things going on which definitely muddies the water. Your comment here suggests to me that one thing you have is a grounding issue - the trailer touching the truck via the ball provides a ground to allow the lights to work and that, conversely, is missing when you're trying to run lights essentially without a ground by not touching trailer to truck. Grounding trailers properly, in my limited experience, is just plain finicky.


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## mrwithers (Jun 25, 2014)

The gooseneck ball should't affect it so if it is you may have a short, loose wire, or corroded connector. Just to double check, there's no battery on the trailer itself is there?

Do you have access to a multi-meter? Measure the voltage between pin 1 and 7 at the point where they connect to the trailer. It should be a little box with some fuses and screws to connect each wire. Pins 1 is the 12v+ wire and 7 is ground. If they aren't labeled you can use the continuity connector on the multimeter to figure out which wire is which.

If you're measuring 12v at that spot pull one of the lights off and measure the voltage between the connectors at that point. If you're not seeing 12v there but you see it at the 7 pin connector it's something between there.

Connectors can get corroded and when it's connected to the gooseneck it could change the contact point just enough that you get this intermittent behavior.

It may also be worth just double checking the fuses. There's a set of fuses for the connector usually on the trailer where the 7 pin cable is wired into the trailer. Should be a little box. It's less likely those got corroded but might be worth checking.

The grounding suggestions are good. If the ground via the 7pin connector is not working then it may be grounding a roundabout way through the hitch itself. Multimeter voltage check should detect that


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## HombresArablegacy (Oct 12, 2013)

Chevaux said:


> I was serious in my other post about multiple things going on which definitely muddies the water. Your comment here suggests to me that one thing you have is a grounding issue - the trailer touching the truck via the ball provides a ground to allow the lights to work and that, conversely, is missing when you're trying to run lights essentially without a ground by not touching trailer to truck. Grounding trailers properly, in my limited experience, is just plain finicky.


This^^^^^ is the problem, your trailer is not grounded when not hooked to the trailer.
_Posted via Mobile Device_


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## waresbear (Jun 18, 2011)

I had the exact same problem, trailer was only 3 years old, I bought it new at that time. Last year, the lights would work intermittently, sometimes only the overheads, sometimes just the interior lights, so I took it into the trailer place. They changed all the fuses in my truck and replaced the surge battery and the trailer plug connection, everything works now.


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## beau159 (Oct 4, 2010)

mrwithers said:


> Just to double check, there's no battery on the trailer itself is there?


Nope. No battery on the trailer. 



mrwithers said:


> Do you have access to a multi-meter? Measure the voltage between pin 1 and 7 at the point where they connect to the trailer.


I have no clue what a multi-meter is but I will ask the hubby! :wink: He's got connections so we maybe can track one down. 

Thanks for the suggestions. Very helpful.


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## horselovinguy (Oct 1, 2013)

Look for a bad ground_ in the plug_***...so if it loses ground the lights quit...if it keeps ground they will work.
When your truck & trailer are connected your trailer is grounding through your hitch so your lights work flawlessly...

_*** you need to check the truck, check the trailer and both parts of the plug. Make sure each wire where it connects to the 7 prongs is a tight fit & connection...they wiggle loose sometimes easily.
Any one of, or the combination will make you pull your hair out in frustration..:evil:

_Good luck!


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## george the mule (Dec 7, 2014)

Hi Beau!

Next time out, take a set of jumper cables. Disconnect the hitch and plug in the trailer as you describe doing. Turn on and off lights until it fails. Leave the switch on, and use the jumper cable to connect between the truck frame, and the trailer frame. If you can't find a clean metal area for the jumper cable, make one with a file or something. The idea is to re-establish the trailer ground with the jumper. If the lights come on when you do this, there is a problem with the ground wire in the trailer electrical harness. Most likely the problem will be where the wire connects to the trailer frame; a loose screw, rust, or bad crimp on the wiring lug. Could also be a nearly severed ground wire, or it could be at the plug, but you say that was just redone. In any event, it is often easier to simply just run another ground wire back from the plug and be done with it. Use the same guage as is in the existing harness, probably 12ga, and screw the trailer end to a clean, protected bare metal spot on the trailer frame. This should resolve the issue.
I will add that if there is a lot of surface rust on the trailer, you may never get a reliable ground thru the frame. In that case, you will have to also install individual ground wires from every light fixture, and to be safe, from the trailer brake backing plates, to a common point where you also attach the ground wire from the plug.

Hope this helps. ByeBye! Steve


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## mrwithers (Jun 25, 2014)

HombresArablegacy said:


> This^^^^^ is the problem, your trailer is not grounded when not hooked to the trailer.
> _Posted via Mobile Device_


It should also ground over the #7 pin on the plug. If that's the issue then fixing the ground pin on the plug should fix it unless the lights in the trailer are grounded to the frame and not the ground pin. In that case then the trailer frame needs to be tied to it or vice versa if the ground on the truck side is broken.


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## PrivatePilot (Dec 7, 2009)

I agree that this is almost certainly a bad ground issue. Trailers that have odd electrical issues when not hooked up (but plugged in only) but then the issues suddenly go away when there's a connection at the hitch end up being ground problems.



george the mule said:


> Hi Beau!
> 
> Next time out, take a set of jumper cables. Disconnect the hitch and plug in the trailer as you describe doing. Turn on and off lights until it fails. Leave the switch on, and use the jumper cable to connect between the truck frame, and the trailer frame.


This is an excellent diagnostic method...the exact same one I use actually.

FWIW, I'm not sure how a shop could possibly have missed this sort of thing - checking ground should be the absolutely positively first thing they do when diagnosing electrical problems. The only explanation is that it was working when they saw it...which sort of fits with your story about how it fails at random after being unhooked. THAT is rather weird as it implies that the ground is going from functional to non functional all of a sudden, but I've seen stranger things happen.

If you can narrow it down to the ground issue using the above diagnostic test (using the booster cables) then that's your issue. Finding out of the ground failure is on the truck side of the trailer side is the next challenge. When the problem occurs this is where using a test light will help probe the issue - check the ground in the 7 pin connector - if it's still alive, then chances are the problem is on the trailer side. In my experience the problem is almost always within the first few feet (up to the first junction) of the electrical cord on the trailer, or the plug itself.


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## beau159 (Oct 4, 2010)

Great suggestions guys, thanks!

I'm almost positive it is a problem with the ground wire with my horse TRAILER because it has done this issue with two different pickups (one of which is pretty much brand new and has a brand new outlet inside the box). 




PrivatePilot said:


> FWIW, I'm not sure how a shop could possibly have missed this sort of thing - checking ground should be the absolutely positively first thing they do when diagnosing electrical problems. The only explanation is that it was working when they saw it...which sort of fits with your story about how it fails at random after being unhooked.


Yeah, it irks me too. 

I've had to two different shops and one of them is considered the best place to go in town (me, I'm not impressed with them). 

I really dread having to take my trailer in for service anymore, because no one seems to listen to me when I explain what's wrong. :evil: So frustrating!

Thanks everyone for your tips. This seems to make sense.


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## PrivatePilot (Dec 7, 2009)

Since its repeatable across multiple trucks, I agree that it's likely on the trailer side. 

I'd start by popping open the electrical plug on the trailer side and investigating. Water gets into them easily and causes all sorts of odd corrosion based issues - it's a very common problem point. The good news is that a replacement plug is neither expensive nor difficult to install.
_Posted via Mobile Device_


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## beau159 (Oct 4, 2010)

PrivatePilot said:


> The good news is that a replacement plug is neither expensive nor difficult to install.
> _Posted via Mobile Device_


The bad news is that a new plug_ was_ just put on about 2 months ago. :? I did have this problem before the new plug was put on. And of course it remains after. 

And I had a new plug put on the trailer when I bought it 3 years ago, because it had a 5-way (?? I think) plug that didn't match hubby's pickup.

I am definately going to try doing jumper cables from the trailer to the pickup, to "ground" it and see if that does the trick.


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## PrivatePilot (Dec 7, 2009)

Have you happened to notice if any of the other lights on trailer continue to work after the interior lights have failed?

Try turning on the clearance or hazard lights when you are experiencing the interior light issue and see if they work still. If they too are not functional and it would definitely point towards a ground issue, however if they are all working normally that it may be something elsewhere.
_Posted via Mobile Device_


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## Corporal (Jul 29, 2010)

Last time we camped at our favorite place in the Black Hills, SD, we had this problem recur. A bunch of other campers tried to help us and we ALL complained about this common problem.
I don't have the best solution but I do have a temporary solution so that you can drive at night and still be seen.
12 Volt Magnetic Towing Light Kit
I went to Harbor Freight and bought myself a set of two lights attached to magnets, and I can hook them to a deep marine battery in my tack room, while attach them to the back of my steel trailer. It won't show your turn signal, they will constantly be on, but you WILL be seen at night, if your connection goes.


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## beau159 (Oct 4, 2010)

PrivatePilot said:


> Have you happened to notice if any of the other lights on trailer continue to work after the interior lights have failed?


This weekend on Saturday night when I had to saddle Shotgun in the dark:
1) Horse trailer was NOT attached to the pickup via the gooseneck ball. It was free standing.
2) I plugged my 7-way trailer cord into the outlet by the receiver hitch. 
3) I turned on my interior dressing room lights and flood light by the dressing room door. They are both on the same light switch. 
4) I turned on my interior lights for the horse section and back flood light, as those are also both on the same light switch. 
5) Any of the side lights on my trailer at NOT on at this point, because the pickup is OFF. 
6) After I haltered my horse and tied him up, I decided to turn on the pickup, so as not to drain the pickup battery (although in all honesty, it really probably is fine for the short amount of time). 
7) When I turned the pickup on, then all the little side lights came on, because the pickup it also running and the lights are "on" on the pickup. 
8) After I was ready to go, I turned off the pickup. 
9) The interior and flood lights all remained on. I turned off both switches when I left to go make my run. 

When I returned:
1) I went to flip the switch to turn on the back flood light and interior lights inside the horse section. I could barely see the smallest little glow from the flood light. 
2) I thought "oh no!" did a fuse blow? Or the pickup battery drain?
3) I tried the other switch for the front flood light and dressing room interior lights. Nothing. 
4) I turned on the pickup. Nothing. Not even the little side lights would come on. Nothing would come on. None of the lights works. I tried unplugged and re-plugging the cord. I tried the outlet inside the box, instead of the reciever hitch. Nothing. 
5) I grabbed my flashlights so I could see what I was doing to unsaddle my horse. 
6) I unplugged my trailer cord from the pickup (still running) so that I could leave to go to my hotel room. 
7) When I got inside the pickup (2014 GMC) the display said to "check trailer wiring". It was 11:00 PM at night and I was too tired to deal with it. So I left. 

The next morning, I hooked up my horse trailer so that I'd be ready to head out once I was done that evening. Lights all worked fine. No problems. 

So for the long answer to your question: *Yes and no. *




PrivatePilot said:


> Try turning on the clearance or hazard lights when you are experiencing the interior light issue and see if they work still. If they too are not functional and it would definitely point towards a ground issue, however if they are all working normally that it may be something elsewhere.


Per my explanation above, the pickup has to be running for any other lights to come on. 

The pickup can be off and my flood lights are still functional (sometimes). 



Corporal said:


> I don't have the best solution but I do have a temporary solution so that you can drive at night and still be seen.
> 12 Volt Magnetic Towing Light Kit


While that's a good tip and something good to have for emergencies, _but as I have said before,_ I do not have a problem when the horse trailer is on the gooseneck ball on the pickup and we are driving down the road. 

I only have a problem when my trailer is *not* lowered onto the gooseneck ball of the pickup, and it is free standing by itself. And I try to plug my cord from my horse trailer into the pickup, in order to turn on my flood lights.


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## PrivatePilot (Dec 7, 2009)

Excellent. Ok, your explanation that when the interior lights didn't work that the clearance lights didn't work either (when you started the truck) screams of a ground issue.

What's causing the ground to be intermittent is the question, but I've seen it happen before. Depending on the electrical load there can actually be quite a lot of current flowing through that ground wire and if it's frayed or has come loose somewhere the heating and cooling cycles from the load/no-load cycles can actually cause it to become intermittent.

The reason you have no issues when hooked up is basically because of what others have mentioned - you're grounding the trailer through the hitch at that point, so the intermittent/faulty ground from the trailer wiring harness isn't essential anymore and things work normally.

So, I'd start looking at the trailer wiring side again - typically the ground wire only goes a short distance before it's attached to the frame somewhere which grounds the entire trailer...and many (but not all) trailers use the frame for grounding. Do you see a junction box or harness box somewhere that the trailer wire leads into? If you can get into that you may very well find your problem in there.


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## beau159 (Oct 4, 2010)

There is a "box" pretty much where the gooseneck attaches to the trailer, and then the 7-way cord comes out of that box. I'll have to open it up tonight and see what it looks like inside.

I know that when I bought my trailer 3 years ago, when we hauled it home the lights didn't work. We took it to the shop and they told us the ground wire was bad and they fixed it. I can't quite recall EXACTLY when I started having trouble with this current problem, but it's been at least a year, but that would kinda be crummy if my ground wire "fix" only lasted a year or two! Or else they didn't fix it all the way. Or else something new "broke".


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## PrivatePilot (Dec 7, 2009)

Once you open up that junction box locate the ground which should be the white wires – if there's nothing obviously wrong inside there it would probably be worth while running a new ground from that main junction to somewhere nearby on the frame. 

Basically you can never have too many grounds, and redundancy can often fix odd issues like this - if the primary ground is being compromised somewhere because of a bad wire or inconsistent connection, a second or third ground mounted elsewhere will often take up the slack. It's basically the same idea as using the booster cables for diagnostic purposes – all you're doing is basically creating another path for the ground to travel through.
_Posted via Mobile Device_


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## beau159 (Oct 4, 2010)

Hmm, I checked the box and everything (as far as my non-electrician eyes can tell) seems okay. 

Ground wire was "dirty" looking with its attachment so I cleaned it up, although that probably doesn't matter?


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## PrivatePilot (Dec 7, 2009)

The black wire On the left in the middle pic (leading to the trailer or to the plug, hard to tell, but it's a ground either way based on where it's connected) looks like it has a taped or possibly repaired section just before it connects to the lug in the junction box - can you peel back that tape or whatever it is and investigate what's going on underneath?

Could be a possible trouble point.
_Posted via Mobile Device_


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## beau159 (Oct 4, 2010)

Yea I looked at that and I should have pulled the tape off to see what was underneath. I was more focused on the *white* ground wire to the trailer. 

I won't be out to the horses for a couple days (going out of town) but I will definately check. 

Really appreciate your advice!


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## PrivatePilot (Dec 7, 2009)

Not a problem glad to help. It looks like there is a nice solid chassis ground coming out of that junction box ( The white wire), however it also appears there is a dedicated ground going elsewhere in that other harness - that black wire that is connected to the same lug. 

When you get back to things perhaps you could post a few pictures of any wiring you can see inside the trailer, specifically the backside of any clearance lights etc where wiring is exposed – I'm curious if the trailer is wired with a dedicated ground to all the lights or if it's like most trailers that relies on a chassis ground. Pictures should be telling – basically if there's only one wire going to each clearance light it is relying on chassis ground, however if there are two independent wires going to each clearance light it changes things a little as it means the trailer is relying on a ******* ground wire pictures should be telling – basically if there's only one wire going to each clearance light it is relying on chassis ground, however if there are two independent wires going to each clearance light it changes things a little as it means the trailer electrical is relying on a web of master ground wires. If everything is relying on a wired ground as opposed to chassis ground the diagnostics change.

Either way I would definitely take a peek under that tape and see what's going on – that looks like a ground wire that leads up into the trailer somewhere and if the latter scenario (where the trailer is relying on a set of grounds to each individual electrical item) ends up being the way the trailer is wired it's definitely highly suspect.
_Posted via Mobile Device_


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## Saddlebag (Jan 17, 2011)

The lights on the two-horse worked intermittently. It turned out the tail light wiring was corroded where it attaches to the bulb housing. New connectors and good electrical grease solved the problem. On our travel trailer, a bumper pull, the pin connector had corroded. I pulled the lights on in the truck and the trailer brakes came on. Check anywhere the wiring is exposed to road grime, rain, etc.


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## beau159 (Oct 4, 2010)

I took the tape off the black wire in the box. I'm not sure why there was tape on it in the first place, it looks totally fine. 











I also looked at the interior lights in the horse section. It appears that there is one wire that runs to each light, and then runs to the next one?

The light in the middle of the horse section:










The light at the back of the horse section:


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## PrivatePilot (Dec 7, 2009)

Ok looks like they're all using chassis ground. Presumably since you were having issues with the clearance lights at the same time as you were the interior lights they too are the same. 

So it comes back to a ground issue somewhere basically. 

The next thing I'd do is try the booster cable ground hack the next time you experience the issue and report back. Try connecting/touching the trailer side of the booster cables to the ground lug on the frame that white wire leads to (the one you cleaned up) and see if that resolves it. If it does then in my mind the problem likely lies in the cable itself between the truck and that junction box...as that would eliminate most everything else.
_Posted via Mobile Device_


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## michaelvanessa (Apr 25, 2012)

*poor earth.*



beau159 said:


> Maybe I'm not explaining things clearly.
> 
> When I have the gooseneck ball attached to the pickup, and the 7-way plugged into the outlet on the pickup, it all works fine.
> 
> ...


sounds like a poor earth (ground wire )issue check your plug clean the contacts with wd 40 or swich cleaner.
as your on the 5th wheel you are grounding the trailer to earth on the pickup so creating the circuit.
try a jump lead off of the pick up and on to the trailer to create an extra earth.


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## beau159 (Oct 4, 2010)

PrivatePilot said:


> The next thing I'd do is try the booster cable ground hack the next time you experience the issue and report back. Try connecting/touching the trailer side of the booster cables to the ground lug on the frame that white wire leads to (the one you cleaned up) and see if that resolves it.


Okay, maybe I totally did the booster cable thing wrong. 

I jacked up the trailer so it was not touching the pickup any longer. I tried using only the black ends of the booster cable from the trailer to the hitch on the pickup. Lights still did not work. 

I then tried ALL the ends of the booster cable and that still did not make the lights work. 

Maybe I didn't connect them in the right spots? I get where you say to touch the tiny nut the white wire connects to (not sure how though, my booster cables seem kinda big?) but then where/what should I connect the other end to on the pickup?


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## PrivatePilot (Dec 7, 2009)

Okay, I'm assuming that the seven pin plug was connected the entire time and that you experienced the issue right from the beginning this time, correct? 

Based on the pictures what you're doing is on the right track, you may just not be getting the cables connected on one end or the other in a place that has good continuity to ground. On the truck side clamp one lead to the hitch ball itself if possible (it's the shiniest and most likely place to provide a good ground) , but clamp the other one somewhere else. Vice versa on the trailer side - connect one end to the frame somewhere, but the other lead somewhere completely different. 

As always try to find somewhere with minimal paint - thick paint can negate a good ground connection. By placing each clip in four distinctly different locations you're helping give the ground a better chance of making a solid connection which is the underlying goal here. 

Based on your photo you have both clamps on the hitch on the truck side and both clamps on the landing gear on the trailer side? If one or the other does not have good continuity to Frame ground it would explain your outcome. 

Keep trying, you're definitely on the right path - I suspect that as you vary the location of the clamps you will certainly suddenly see all the lights come on. Don't be afraid to try all sorts of different locations for all four clamps as well as wiggling them around while somebody else watches the lights


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## CBXSteve (Apr 28, 2015)

Hey Beau,

In one of your pictures, you show a plastic box mounted in the overhang frame above the junction box. THAT is very likely a battery box. 

Bear with me here:

The purpose of the battery that is supposed to be in that box is to power the electric braking system in the event of the trailer disconnecting from the vehicle. If you have electric trailer brakes, you will have a steel tether cable which connects to a switch. If the trailer disconnects from the truck, the tether pulls the plug out of the switch, which applies the battery power to the trailer brakes. Perhaps you knew all that but don't have trailer brakes....

I am an electronics technician, and have precisely the same problem you do with my gooseneck trailers. I troubleshot mine, and concluded it was not a grounding issue.

I have not taken the time to fully troubleshoot and fix this problem yet, but I have a working theory as to what is going on, and a solution in mind to fix it. At the risk of muddying the water in here even more, I will share them.

Theory: I believe the root cause of the problem is that my 2005 Silverado 2500HD w/towing package does not constantly supply 12V power (or ground, pick) to the trailer while the truck is not running. I further believe that this is by design to prevent trailer braking batteries from draining the vehicle battery while connected but not running, and that the truck computer is turning off that power (or ground) by some formula that I have not been able to figure out.

My solution: When I get time, I am going to wire my trailer utility lights to my braking battery so that even when the truck is disconnected, the lights will work.

If you choose this solution, and do have electric brakes, you will need to be careful NOT to drain your braking battery inadvertently, but if you don't have electric brakes, it looks like you have a battery box, with maybe a battery inside, to use in this way.


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## PrivatePilot (Dec 7, 2009)

Breakaway battery system issues wouldn't effect the rest of the lights however. The issues are occurring across the entire electrical system, not just the parts that the aux trailer circuit would cover...which are indeed the breakaway battery and often interior lighting. 

If the issues were limited solely to the interior lights while all other lights worked normally I'd be suggesting more attention to the aux circuit wiring but it seems like a grounding issue based on all the symptoms.


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## CBXSteve (Apr 28, 2015)

PrivatePilot said:


> Breakaway battery system issues wouldn't effect the rest of the lights however. The issues are occurring across the entire electrical system, not just the parts that the aux trailer circuit would cover...which are indeed the breakaway battery and often interior lighting.
> 
> If the issues were limited solely to the interior lights while all other lights worked normally I'd be suggesting more attention to the aux circuit wiring but it seems like a grounding issue based on all the symptoms.


Ahhh, I missed "Returned item 4" on post 24. Clearance light dim. You are correct.

Or maybe the dim clearance light issue was grounding and the utility lights are the mystery supply relay. Two separate issues muddying the waters?

Ok, I will step quietly away here. You have the airplane.


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## PrivatePilot (Dec 7, 2009)

Being repeatable across multiple tow vehicles is the other indicator that made me virtually rule out the issue possibly being something on the truck side As well.


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## beau159 (Oct 4, 2010)

PrivatePilot said:


> Okay, I'm assuming that the seven pin plug was connected the entire time and that you experienced the issue right from the beginning this time, correct?


I had just returned home from a barrel race. Lights worked fine while I was hooked up the pickup (both the 7 pin plug and the trailer resting on the gooseneck ball). I tried this experiment when I got home, and had unhooked the trailer and jacked it up off the ball, but left the 7 pin plug still plugged into the pickup. 



PrivatePilot said:


> On the truck side clamp one lead to the hitch ball itself if possible (it's the shiniest and most likely place to provide a good ground) , but clamp the other one somewhere else. Vice versa on the trailer side - connect one end to the frame somewhere, but the other lead somewhere completely different.
> 
> As always try to find somewhere with minimal paint - thick paint can negate a good ground connection. By placing each clip in four distinctly different locations you're helping give the ground a better chance of making a solid connection which is the underlying goal here.


Maybe their was too much paint on the brand new receiver hitch on the pickup. :wink: I can try putting it right on the ball. 

For the trailer side, I chose that area on the jack, because most of the paint is rusted off .... unless rust is not a good conductor?




PrivatePilot said:


> Based on your photo you have both clamps on the hitch on the truck side and both clamps on the landing gear on the trailer side?


Yes. In this picture, I have both ends attached to their respective side (picking and trailer). 

I did not take a picture, but I did try ONLY the black clamp ends only, but with the same result. I wasn't sure if I needed both clamps so I tried it both ways. 


If one or the other does not have good continuity to Frame ground it would explain your outcome. 



PrivatePilot said:


> Keep trying, you're definitely on the right path - I suspect that as you vary the location of the clamps you will certainly suddenly see all the lights come on. Don't be afraid to try all sorts of different locations for all four clamps as well as wiggling them around while somebody else watches the lights


Thanks, I will have to drag hubby out with me and we'll see. 

It's just really making sense that it is a ground wire issue though. Because, trailer lights worked find until I jacked it up off the pickup ("the ground source) and off the gooseneck ball. Then they didn't work.


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## beau159 (Oct 4, 2010)

PrivatePilot said:


> Being repeatable across multiple tow vehicles is the other indicator that made me virtually rule out the issue possibly being something on the truck side As well.


Correct. It does it with both the 2014 GMC (3/4 ton) we have and the 2009 GMC Sierra (1/2 ton) that we have.


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## CBXSteve (Apr 28, 2015)

PrivatePilot said:


> Being repeatable across multiple tow vehicles is the other indicator that made me virtually rule out the issue possibly being something on the truck side As well.


Add my vehicle and 2 different gooseneck trailers to the mix on the utility light issue. Having said that, you are pretty clearly on the track of something else...continue sir!


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## PrivatePilot (Dec 7, 2009)

Ok...on the right track. Experiment with those cables and different grounding locations all over the place on both the truck and trailer side. One cable or both cables, doesn't matter, clip them here there and everywhere, as long as you don't connect them to positive power anywhere you can't cause any harm whatsoever. 

Eventually you're apt to find the magic combination that lights things up and you've basically confirmed the ground issue at that point. 

Once you find a good solid ground on the pick up truck try connecting the opposite end of ONE of the booster cable leads (you want to start to narrow things down at that point) to the ground lug near the junction box on the trailer that you shined up earlier in the thread. If everything lights up again at that point you have basically 100% confirmed the ground issue, but also narrowed down the exact source of the ground problem to one of two things – either the electrical cord on the trailer itself is problematic, or there is no ground being fed to that cord by the truck. I think that possibility is low simply because of the fact the issue was repeatable across multiple trucks, however before condemning the cord on the trailer I would want to do a ground continuity test on the plug on the truck just to 100% confirm it first - it would suck to replace that cable on the trailer only to find the problem is still there - we want to exactly eliminate all possibilities and pinpoint the issue first before starting to fix anything. 

Although it's unlikely you have ground issues on the truck receptacle on both trucks, nothing is impossible...and it's a reasonably easy test. 
_Posted via Mobile Device_


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## mred (Jan 7, 2015)

If you had a ohm meter, it might be easier. I have seen trucks, a lot, that did not have the ground wire connected to the plug. The person that installed it,"it will ground thru the hitch". At the same time I have a trailer that the ground wire was not connected. My inside lights only work with the truck lights on. The brake battery is charged by the brakes and not by the hot wire from the truck. My battery wire from the truck, ends in a juction box under the trailer. not used. I had a problem and found that wires were loose in the plug. Someone had pulled the plug out by the cable.


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## PrivatePilot (Dec 7, 2009)

The breakaway battery is absolutely positively supposed to charge from the aux circuit – if it's set up any other way somebody has rewired the trailer. There is no other circuit that can carry the correct amperage to recharge the battery in a timely fashion, nor one that is on long enough during a haul to accomplish it - even then most people find that there breakaway battery is often dead or extremely depleted as most people do not haul often or far enough to properly charge it. 

If your interior lights only work with the clearance lights on that's just the way the trailer is wired as well – mine is wired this way but I would much prefer that the trailer lights be powered from the auxiliary circuit as I wouldn't need to leave all the (wasteful) clearance lights on when loading/unloading in the dark killing my truck batteries in the process.
_Posted via Mobile Device_


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## gypsy cowboy (Jun 27, 2015)

beau159 said:


> Let me add that when the trailer is completely hooked up to the pickup, I've never had a problem with the lights.
> 
> It's just when I need to unhook the pickup ... but still have my flood lights and dressing room lights turn on.
> 
> ...


That it Only happens when you are un-hitched almost guarantees it's a "grounding" issue. That can trick you because it can be intermittent. Sometimes work sometimes not. That's the quirky nature of electrical grounds, depends on how you hold your ears :wink:

Simply clipping a set of battery jumper cables from your hitch to solid grounded contact on your truck, somewhere on the bumper or its hangers... would likely eliminate your "unhitched" light problem.

It also says that the "Ground" wire through the 7-way likely isn't properly connected - somewhere - which then requires the trailer to be in contact with the truck through the ball to be able to complete the necessary circuit to the batteries to power your lights.


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