2014 gmc trailer plug wiring

sundj15 · August 22, 2015

I haven't seen a post about this, probably because I've been searching the wrong words but hopefully someone has something.

I have hooked my truck up to 3 trailers. 1 was just rewired and the other two work with other trucks.

My problem is that if I drop the tongue on the ball with it plugged into truck, the lights on the trailer flicker when the tongue moves on the ball. Note that I have just bought a new nickel ball unit.

With the trailer off of the hitch but still plugged in the lights do not flicker, they work normally.

Not sure what the issue is. Anyone have any thoughts?

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bdbake01 · August 22, 2015

Sounds like you have a mild short between hot (parking lights probably) and the trailer frame providing ground. The trailer frame (ie, ground) gets tied to the vehicle ground via the ball when hitched, and there's your short. The problem doesn't present itself when unhitched since the circuit isn't complete.

Frustrated2 · August 22, 2015

From experience on many vehicles, I can gurantee you your problem is a poor ground. From you description of the problem, you are trying to ground thru the trailer hitch ball. This is an inadequate way to do it. Your connecter plug should have a separate ground wire (green) that attaches to the trailer frame. If you have this wire and are still having a problem, check where the wire attaches to the frame or tongue of the trailer..

Another spot to check is if you have a tilt trailer and the ground wire attaches to the trailer tongue. Sometimes in this configuration, the piviot point between the tongue and the actual frame of the trailer may be the problem. connect another wire between those two points. It's a good idea to use a little dielectric grease (available at autoparts stores) on the connector and the ground wire attachment point. Make sure all the connections are clean before applying. Good luck.

Rme2513 · August 23, 2015

Ground wire is white on a trailer plug and yes I to would say it's the ground check where it connects to the tongue and if that does not work check the lights most of the ground threw the bolts that hold the light on clean the paint off for a good connection and put some dielectric grease on it if that does not work pull new wire. P.S. A short is a path to ground witch causes a fuse to blow an open is a cut wire witch causes no current to be able flow ( no lights )

sundj15 · August 23, 2015

Does it make sense that these trailers that were used, work on other trucks just fine? Would there be a problem with the trucks trailer harness?

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Rme2513 · August 23, 2015

does it do this to all trailers or just a few? I would find a new trailer and hook up to it and see bad grounds can do some very wired stuff but if it's all trailers I would say it was the truck and check its trailer ground wire and if it goes into a plug splice a wire into it before the plug (white wire) and go straight to the frame make sure it's clean metal where you attache it to

jagabom (Esquire) · August 25, 2015

If the other trailers work good on your truck, that trailer probably has a short. If the other trucks balls are old and rusty, current may not be able to flow threw them. Your ball is new and may allow current to flow through. Plug in the trailer to your truck. Don't hook up the hitch. Turn the lights on. Make sure the voltmeter is good by first hooking it up to a 12 volt battery. Should read 12 volts. Run a volt meter from the tongue to the ball or better yet a good ground on the truck. Make sure you get good contact. If you get voltage then there is a problem. Not sure if it is the truck or trailer but if it doesn't happen with the other trailers it is probably that trailer. Should be zero volts. Just make sure you make good contact with the leads of the voltmeter or results will not be right. Is it just the running lights or do the brake lights flicker to? Turn the running lights off, apply the brakes enough to turn them on and drive around. You could do the same test with the other trucks. Don't hook the voltmeter up to the ball but to a good ground on the other truck. If you get voltage then the trailer is suspect. I hate automotive wiring. lol

Jim