# Need help with 7 pin wiring - replaced on horse trailer side and not working!



## loosie (Jun 19, 2008)

My husband saw my float indicators weren't working recently & decided to fix it... then I found I had no lights. Turned out, the wires were... a over t on the trailer, so when he wired them up correctly at the plug, they were... wrong! Unfortunately as he didn't tell me he'd done it, I spent ages looking elsewhere for the fault!


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## trailscout (Nov 23, 2020)

Believe it or not, 7 pin color coding is different for RV trailers and horse trailers which come under utility trailers.

I bought a horse trailer that had the cable with the connector replaced with an RV cable. When I was rewiring it, I was concerned about all the wiring not matching.

Went to the wonderful world of the web and found pictures of the RV color code and utility color code. Printed out both and used them to match up the differing colors. Everything works now.

This may or may not be your problem.


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## george the mule (Dec 7, 2014)

Hi LLLR

Yeah, there are two common wiring arrangements, and many "homebrew" setups where the owner either didn't have the correct cable, or didn't know/care about the standard. I'll attach a drawing of the common two:








However, that said, a very common problem is a bad ground, and that would be the first thing on my list of things to check. Remember, the white wire is ground on a trailer. Verify that it is physically attached to the trailer frame.

If you get stuck, let me know, and I will try to walk you thru troubleshooting your system; you will need a cheap multimeter, and preferably an analog one (meter with needle).

Hope this helps

edit to add: I have three trailers that use a 7-pin; two horse trailers and a flatbed car hauler. They all have the "traditional" arrangement, none have a backup light, and only the GN horse trailer uses the +12v pin.

PPS: I lied; both horse trailers have +12v wiring; the old BP trailer has a short somewhere, and the interior lighting circuit is disconnected


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## horselovinguy (Oct 1, 2013)

What you wire for the plug must match the receptacle or you have issues.
As that above diagram showed....there are many ways to wire "correctly" but there are different variations baed on plug intention/designation..
Make sure your grounds are solid and secure too or that can throw you a issue too.

Any trailer we've ever bought, hubby yanks the lights apart and wires the same for every vehicle so plug & go works.
From enclosed car haulers, to open flatbed to our horse trailers....all had the same wires in locations for all to work properly.
He only ever uses the 7-pin HD plug too...
🐴...


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## livelovelaughride (Sep 13, 2011)

Hi, just checking in and great to see some things to try this morning... 
Its a drag we can't see the interior of the old plug.
But I also wonder if the truck side wiring could be part of the problem. Its a 2010 Ford Sportrak. I'd have thought that 7pins on the truck side were universal....And, where I have my trailer parked there is another horse trailer next to it. I guess we could sneak over and see if that truck powers up that trailer.
Report to follow....
thanks to you all for your suggestions!!!


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## trailscout (Nov 23, 2020)

Also will mention although you and/or your hubby likely already know, trailers that have set around without any vibration going to the light sockets often get corroded and lose contact. Fix for that is normally to remove the bulb, maybe scrape around a little and re-insert. That is for the older trailers with the round brass end on the bulb with two little ears. Newer ones may not offer that problem.


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## george the mule (Dec 7, 2014)

livelovelaughride said:


> But I also wonder if the truck side wiring could be part of the problem. Its a 2010 Ford Sportrak. I'd have thought that 7pins on the truck side were universal....And, where I have my trailer parked there is another horse trailer next to it. I guess we could sneak over and see if that truck powers up that trailer.
> Report to follow....
> thanks to you all for your suggestions!!!


That might be useful, might not. Is there anyone at your barn who has a horse hauler that you can plug _your_ trailer into? If it works on a different vehicle, the problem is in your truck for sure, if not, it's your trailer wiring. However, seeing as nothing is working on yours, I'd start by checking the ground wire. Note that it is in the same spot on both Traditional, and RV setups. If you don't have the ground, nothing will work, or worse, it will work intermittently via a ground thru the ball/hitch assembly.
What you need to get first off is one of these:








Sperry Instruments HSP5 5 Function Analog Multi-Meter, Manual 13 Range, 300V AC/DC - Multi Testers - Amazon.com


Sperry Instruments HSP5 5 Function Analog Multi-Meter, Manual 13 Range, 300V AC/DC - Multi Testers - Amazon.com



www.amazon.com




Armed with this, it is real easy to test the receptacle on your truck. I think you can also get a dedicated tester you can plug in, with LEDs that illuminate when the truck lights are activated, but the multimeter is a more useful device in the long run.
And I strongly suggest the analog meter. A digital one can give misleading results, whereas with the old-school ones, if the meter needle moves, you can be reasonably sure there is voltage or continuity in the circuit you are testing.
Just FWIW, I used to get handed the Freshman/Sophomore Circuits lab from time to time. I would lock up all of the newer instrumentation, and equip the stations with an analog multimeter similar to the one shown (only even cheaper ones from Radio Shack), and dusty old analog oscilloscopes. Students coming out of my class knew more about the tools they were using than just how to push an "autoscale" button, I can promise you that. More than some of the tenured professors in the department as far as that goes. Don't get me started . . .


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## horselovinguy (Oct 1, 2013)

Have you ever trailered with this truck before?
Did lights and brake controller work then?
If the truck is "new" to you and this new job...
Sounds ridiculous but check to make sure there is a fuse and it is the right size and not blown too....
Many go after thinking major and it was a missing or blown fuse is not uncommon.
I so hope this is a simple fix for you...
🐴...


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## livelovelaughride (Sep 13, 2011)

I'm just a little exhausted (cross eyes). Hubby could not get the configuration to work (its the photo with the NG marked on it). He gave up and so I have spent the last two and a half hours whittling down the original connector. The truck and the old connector seemed a bit finicky, I put it down to corrosion.

It had worked fine the last two times out, but I had to fiddle with the blades/corrosion for a half hour, thats why I wanted to replace the 7 pin on the trailer. The truck 7 pin had been fine with another trailer recently. But I will keep it in mind too!
So....the drawing is of the original 7pin, facing away. It looks like, from the top going counterclockwise: green/red/white ground/blue/brown/black and I hope the center is yellow. With the 7 pin face on it would be opposite.
I believe my hubby tried both directions.
Anyway if this was the original configuration it should work. Does anyone see a different configuration from my photos?The black wire got a little sliced up and its clear to me the yellow goes behind it. TIA!
Edit to add: yes brake controller and lights/signals did work. One of the pins from the original 7 pin (they are like clips) was sitting too low and I thought would not connect properly hence the fiddling.


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## livelovelaughride (Sep 13, 2011)

George: I printed out yours as well and hubby tried it, along with another one I got off the web for "circle J"...both didn't work. 
I will attempt to check on this myself tomorrow and see....
I also talked to the dealer I bought the trailer from - I couldn't find the schematic he mentioned on the web.


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## george the mule (Dec 7, 2014)

Hmmm. The wire colors and arrangement match the RV connector. Never the less, the circuits are all on the same pins, only the wire colors change, so it shouldn't really matter. Try connecting a 12v battery from the white "ground" wire to the red, brown, and green at the back of the new connector. You should get the left turn/brake, right turn/brake, and tail/running lights to come on. Just use 2 lengths of wire with the insulation stripped from the ends, and be careful not to short out the battery. Really helps to have someone watch the trailer lights while you work the jumper wires. If the wrong lights illuminate, note which wire gets which light. If you still get no lights, try connecting to the trailer frame (use a file to get down to clean bare metal) instead of the white ground wire. Still no? try connecting the battery between the white wire and trailer frame. Should get a fat spark, and probably the wire will get hot. Still no? Bad connection where the white wire connects to the frame. (Again, a very common failure point.) Yes spark, ground probably OK, and you'll need to check the individual tail lights, and the wiring running to them. The horse trailers I have had all had a small fuse box, generally near the floor in the tack room. Follow the big cable back from the plug and you should find it. Check the fuses. Follow the wires on back from the fuse box to the tail lights; be sure they aren't broken, pinched, or shorted to the frame. They will probably run inside the frame member, so use a screwdriver to un-mount the tail light assemblies, and check there. Wire colors should match. If you connect the battery to the brake wire, someone with their ear to one of the rear wheels should hear a pretty loud "clunk" as the brake magnet energizes. Backup light and interior lights (+12V)? Just leave those wires disconnected until you get the important ones sorted.

Go to etrailer.com for most anything trailer related. Here is a link to the wiring page, and you should find some trouble-shooting info there as well.



https://www.etrailer.com/faq-wiring.aspx


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## livelovelaughride (Sep 13, 2011)

Thats a little daunting...but i plan to replicate the old config to the new. Make sense? Thanks though for the help. If i can't figure it out I have a buddy...


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## george the mule (Dec 7, 2014)

Well, yes; the new plug should have every wire connected to the same terminal as it was on the original one. But I thought you said you had tried that already?
Where did you get that last diagram; the one that says "PJ Trailers"? 
Note that the wire colors shown are different from either of the standard configurations. Is this the OEM wiring diagram for the trailer, then? Did you buy the trailer new, or used? If used, perhaps someone has already replaced the plug with one from an RV, and made the necessary wiring changes somewhere along the main cable. Do you see an obvious splice? Would be a thicker spot with electrical tape or heat-shrink tubing covering it. Did something like that get cut off when your OM originally replaced the plug?
Whatever, you first need to determine which wire goes to each light on the trailer, and verify that the light comes on when supplied with 12V. Then connect that wire to the appropriate place on the plug and check it again. Then connect the plug to your truck and test to see if they work. As you have at this point verified that the trailer lights are working as far as the plug, any issues are coming from the truck. Is the brake controller in the truck a factory install? If so, you can safely assume that the wiring to the receptacle follows the standard format. Probably so with an aftermarket install as well, but less absolute.
Brake controllers vary, but the ones I'm familiar with do not pass the light-on signal straight thru, but have their own relay for trailer lights. This is to prevent the trailer electrical load from affecting the tow vehicle lights. These controllers do fail. Once you arrive at this point, it's probably worthwhile to plug in a different trailer to see if the same failure occurs. Diagnosing a fault in the vehicle wiring is far more troublesome, and beyond the scope of a forum topic, I'm afraid. Look for an in-line fuse in the wire from the battery to the brake controller, maybe . . . But just assume it works until you are certain the trailer isn't the culprit as per the above. You absolutely have to define something as "Known Good" to be able to address that which is unknown.
'Bout all I can offer . . . Steve


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## trailscout (Nov 23, 2020)

I have a multi-tester and am comfortable with it. But if you're not, just a simple 12v tester will tell you if you have current in a completed circuit. One end on the hot wire and one end on ground.


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## livelovelaughride (Sep 13, 2011)

Just a quick note of thanks, everyone, and a successful wiring configuration. It seems the one I got off the web detailing a Circle j trailer - was correct but didn't indicate whether it was front facing or the back. It is the same configuration as the picture George provided, the Trailer Side 7 way, middle pic, and in this case the purple brake controller wire was blue (for me).
I might invest in a 7 way tester at some point. And I will keep the old 7 pin for reference if I ever have to replace the truck 7 way pin as they have to match.
Note: The PJ Trailer diagram was off the 'net and supposed to be a livestock trailer config. It didn't work for my trailer. My trailer was bought new and set up both truck and trailer side from a trailer dealership, so OEM all aspects.
Have a good night!


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