Trailer Brake Harness

[carbonvoy]

I just picked up a new '05 Envoy XL SLT with a 5.3L. When I picked it up, I went into the parts counter and asked for the wire harness that connects an electric trailer brake controller to the vehicle, since it is wired with a 7 pin connector, and I have a camper with trailer brakes. The parts guy looked and said GM doesn't make one. :confused: I told him I had bought one from GM for my '03 Sierra Z71, which I still own, so that makes no sense.

Is it possible GM produces this vehicle with a 7 pin wiring connector, which obviously includes trailer brakes, then doesn't make the plug in harness to connect the trailer brake controller? Anyone else had this problem and solved it?

[ScarabEpic22]

I know in my 02 that there are 4 wires under the dash with a piece of paper telling you what each wire is for, and you just connect these wires to the trailer brake controller, and you are done. I have heard rumors about a wire harness, but everyone I have talked to said they dont need it.

I think there is a thread about this somewhere, I will look and find it for ya. :)

[ScarabEpic22]

Found it!

http://forums.trailvoy.com/showthread.php?t=264&highlight=trailer+controller

Hope this answers your question.

[carbonvoy]

Thanks Erik - I searched for threads and couldn't find one. I hope you are more successful than I was. I thought it might be under the dash already, so I've been under there with a flashlight, and I can't see it.

[carbonvoy]

You beat me! Thanks, I'll look at it.

[ScarabEpic22]

...I thought it might be under the dash already, so I've been under there with a flashlight, and I can't see it.


They are taped to the big bundle of wires (that are on the left of the car) to the inner side of them.
It took me a few minutes of looking to finally find them when I installed my controller last spring.

[Benvoyage]

I put an adapter on my 03 Envoys prewired wiring harness and I am not recieving a parking light signal when testing the factory harness. I have the plug that converts to a 4 prong and the brakes, left sig, and right sig, work but the parking lights arent. Anyone had this prob or can help me with mine? thanks!!

[EnvoyXL]

I dont have a right parking light on mine, but when I hook my trailer up to another truck the lights work.

[jwstewar]

I dont have a right parking light on mine, but when I hook my trailer up to another truck the lights work.

Do you have a left parking light? If so, it isn't your tow vehicle. You only have one wire for the parking lights going to the trailer. It is then split on the trailer. Check your grounds. Looks like the right is trying to ground through the trailer and then your trailer is trying to ground through the ball - not a good way to do it. If you don't have a ground wire on the trailer harness going to the tow vehicle - add one. If you have one try cleaning up the connection. Other wise it could just be the light itself going bad. I have one doing that myself on my little trailer. Sometimes it works, sometimes it doesn't. I've messed with it to fix it, but doesn't last too much bouncing. I think I'm just going to rewire the whole thing this summer when I have time.

[the roadie]

I put an adapter on my 03 Envoys prewired wiring harness and I am not recieving a parking light signal when testing the factory harness. I have the plug that converts to a 4 prong and the brakes, left sig, and right sig, work but the parking lights arent. Anyone had this prob or can help me with mine? thanks!!

Could be the adapter or the fuse in the vehicle. The trailer harness turn signals and parking lights are separately fused. Check the owner's manual. The adapter should take pin 3 from the car and send it to your parking light wire (brown if they followed the standard color code)

http://www.etrailer.com/Merchant2/graphics/00000001/hh/ele/wiring_7pole.jpg

[600rrjoe]

my 04 came with the elctronic brake control harnes, of course they handed it to me and said you install it.

[zamar]

Here is a helpful link too:

http://envoystuff.com/index.php?showtopic=40&hl=trailer

[EnvoyXL]

Do you have a left parking light? If so, it isn't your tow vehicle. You only have one wire for the parking lights going to the trailer. It is then split on the trailer. Check your grounds. Looks like the right is trying to ground through the trailer and then your trailer is trying to ground through the ball - not a good way to do it. If you don't have a ground wire on the trailer harness going to the tow vehicle - add one. If you have one try cleaning up the connection. Other wise it could just be the light itself going bad. I have one doing that myself on my little trailer. Sometimes it works, sometimes it doesn't. I've messed with it to fix it, but doesn't last too much bouncing. I think I'm just going to rewire the whole thing this summer when I have time.

My left trailer light works, but not the right one. When I hook my trailer to my tahoe they both work, so that tells me it is the vehicle. I use the same wiring adapter for both vehicles so it cant be that either. the only thing different is the vehicle. Envoy=only left light, Tahoe=left and right

[jwstewar]

Is it parking light or turn signal/brake light not working? It can't be only one parking light working and be a tow vehicle problem. Look at the diagram Roadie posted earlier. 99.9% of all trailer lighting problems are ground problems.

[chevy350]

My left trailer light works, but not the right one. When I hook my trailer to my tahoe they both work, so that tells me it is the vehicle. I use the same wiring adapter for both vehicles so it cant be that either. the only thing different is the vehicle. Envoy=only left light, Tahoe=left and right
I have the exact same problem with my '03 TB
did you find the problem

[EnvoyXL]

I never looked into it. It doesnt really bother me enough since I very seldom tow anything.

[kendico]

Four wires under the dash, (orange, black, light blue, dark blue) just above the dead pedal, ready to be wired to your controller. There is no plug, but can be easily wired by a novice.

[poom]

My left trailer light works, but not the right one. When I hook my trailer to my tahoe they both work, so that tells me it is the vehicle. I use the same wiring adapter for both vehicles so it cant be that either. the only thing different is the vehicle. Envoy=only left light, Tahoe=left and right


I dont use my wireing for a trailer, but I have a led lightbar and only the left half works when brakes are applied. Turn signals, parking lights work fine. I went out and got another NEW led lightbar thinking it was damaged, hooked it up and I still have the same problem. I havent had time to look into this problem yet :undecided. If you find anything out please post back. Might call the dealer on this one....

[ScarabEpic22]

I dont use my wireing for a trailer, but I have a led lightbar and only the left half works when brakes are applied. Turn signals, parking lights work fine. I went out and got another NEW led lightbar thinking it was damaged, hooked it up and I still have the same problem. I havent had time to look into this problem yet :undecided. If you find anything out please post back. Might call the dealer on this one....
Does the right turn signal flash? If not, then its a fuse. If it does, time for the dealer.

[Gary UT]

Check the fuse box under the hood.

Fuse 50 is the right side trailer turn, 51 is the left.

I had the same problem when I picked up my trailer.

The flashers on the vehicle will still work with the trailer turn signal fuses blown.

Gary