2001 2500hd Trailer Wiring Problem

billy · June 4, 2007

hi, i'm new to this forum and i had to post 5 replys in another thread to get this tread going..sorry for that problem is:

all the lights work on the trailer, but when i have the running lights on AND i use a turn signal left or right doesn't matter, both the left and right side blink. What i think is actually happing is that the side that is NOT supposed to blink is going dim...each side has dual filament and one of the filaments goes dim making it appear to blink too.

i bought the truck used and i just got a trailer so i don't know if it's been like this for 6 years or not.

i eliminated the trailer wiring by hooking up to different trailer and had the same problem so i know the problem is with the truck.

the truck has the tow package and i cleaned and checked the connector at the bummper also took the back side of the connector off and cleaned and reseated it. the positive battery post was horribly corroded so i cleaned and polished and put dyelectric grease on it, i took a quick look under the engine bay fuse panel and found no apparent lose wires.

has anyone had this problem it's driving me crazy.

Webb · June 4, 2007

Do you have a test light? If so try turning on the headlights. then connect the clip to the to the odd connector (if its a 4-way flat) then probe the hole right next to it. This will make sure the ground is good on your harness. If thats good, hit the left turn and test the hole next to the one you just tested, it should blink. then test the right turn in the last hole. If none of that worked try clipping the testers clip to a chrome part on the bumper or a cleanish bolt one the hitch, might have to scrape the rust off the bole to make sure you get a ground (chrome works alot better if you have it. Then repeat the test. If that way works and the first way didnt, then the ground on the harness isnt connected. If its a 7-way round connector I gotta get back to you on what terminal is what one that one, its been a while

Burbman · June 4, 2007

Here are the 7-pin diagrams. use a test light or meter to troubleshoot.

Russ Huelle · June 6, 2007

I am new and am having a similar problem with my factory trailer wiring.

I just bought a 2001 Chevy 2500HD 4x4 with the 8.1 and 6 speed manual and I have to say I love it.

Now for my problem. I have all lights on 2 different trailers exept break lights. I still have the factory plug out the back of the truck and there was a trailer break controller installed and pluged into the port under the dash. I used an idiot light on the plug itself and on the wires in front of the plug and have power on the wires that are for the turn/stop on both the right and left side but nothing when I step on the break. I have looked at all the fuses under the hood and in the dash by the door and they all look good. Does anybody have any helpful hints I can try before I have to take it in to have it looked at.

Webb · June 6, 2007

100%Chevy, does the left and right terminals blink when you turn one your flashers, and then stop when you push the brake?

billy · June 8, 2007

thanks for the replies guys! i forgot to mention that i tested the crap out of all the pins...got the plug in tester the whole 9.... and they are all correct....and the problem does NOT show up on the plug in tester......that's the kicker. the lights shouldn't work at all if the ground isn't grounded right? ....anyways i'll let ya know when i get it fixed.

billy · June 8, 2007

Do you have a test light? If so try turning on the headlights. then connect the clip to the to the odd connector (if its a 4-way flat) then probe the hole right next to it. This will make sure the ground is good on your harness. If thats good, hit the left turn and test the hole next to the one you just tested, it should blink. then test the right turn in the last hole. If none of that worked try clipping the testers clip to a chrome part on the bumper or a cleanish bolt one the hitch, might have to scrape the rust off the bole to make sure you get a ground (chrome works alot better if you have it. Then repeat the test. If that way works and the first way didnt, then the ground on the harness isnt connected. If its a 7-way round connector I gotta get back to you on what terminal is what one that one, its been a while

it's the factory 7 spade

Webb · June 8, 2007

Did you try grounding it inside the plug? Like truning the headlights on and touching the bottom left to the top left tail light lead. Dont let that diagram throw you off, its backwards, youd want to look at the one labeled trailer for testing your truck. Well it just apears to be backwards caus its veiwing from the backsides of the connectors, if you were looking at it standing behind your truck it would be the other way around.

Also what kinda trailer is it? I know its not too likely if you tried another trailer and got the same problem, but not entirely imposible. That would be the way it looks if your truck connector tests out 100%. Make sure your using the ground inside the 7-way. also another way to test it is by hooking up the trailer and cliping the test light on to the trailer frame and touching the trucks bumper with the other end. to see if the light lights up, it shouldnt if its grounding properly.

it may be that both trailers need to be wired for a ground. not all trailers are wired that way. Some of them rely on the trailer tounge to hitch ball ground, but this doesnt always work. Like if there is corrosion or something.

Another thing ive seen far too many that just ground the trailers lights to the back of the tralier frame and then maybe pick up the ground again at the front of the trailer relying one the tralers fram to carry the ground signal. witch works pretty good accept on those tralers that fold up in the middle, they tend to loose the ground at that joint after a few years of road salt.

billy · July 26, 2007

haultruck=me

.......WOW....I'M STUPID!!!! well the problem was that i didn't have the ground on the right pin on the trailer connector. thanks for trying to help me out and i appologize that you guys wasted your time.

gmtjeff · July 26, 2007

thanks for the replies guys! i forgot to mention that i tested the crap out of all the pins...got the plug in tester the whole 9.... and they are all correct....and the problem does NOT show up on the plug in tester......that's the kicker. the lights shouldn't work at all if the ground isn't grounded right? ....anyways i'll let ya know when i get it fixed.