Trailer lights kinda working?

[PapaHepcat]

I had to wire up my truck for pulling a TT (dealer told me it already was, and I was dumb enough not to check). I got it all wired up and everything. Tested it all with a simple tester and everything works in the plug as it should.

Problem is, when I test the trailer lights when plugged in, the left turn signal / brake doesn't work. I used a battery and tested the connection at the trailer plug, and the light comes on just fine.

So what gives? Everything tests fine on the truck plug. Everything tests fine at the trailer plug. But when together.

*Edit: a couple of theories...
1) maybe my ground on the plug wire isn't robust enough for all the wiring? I tapped it to another ground.
2) In testing the truck, I found the 12v battery power isn't getting juice. I'll fix that. But would that even be related?

[Belgian]

Check the ground wire on your trailer. Most will come out of the trailer plug and go to a frame bolt. Also the ground for the light may be loose. Try taking a jumper wire from the truck frame to the trailer frame and see if that helps. When we pulled a trailer we often had the same problem. Our trailer needed the truck ball/trailer hitch for additional grounding for everything to work right.

[Funkmoney]

Quote:

Originally Posted by PapaHepcat I had to wire up my truck for pulling a TT (dealer told me it already was, and I was dumb enough not to check). I got it all wired up and everything. Tested it all with a simple tester and everything works in the plug as it should. Problem is, when I test the trailer lights when plugged in, the left turn signal / brake doesn't work. I used a battery and tested the connection at the trailer plug, and the light comes on just fine. So what gives? Everything tests fine on the truck plug. Everything tests fine at the trailer plug. But when together. *Edit: a couple of theories... 1) maybe my ground on the plug wire isn't robust enough for all the wiring? I tapped it to another ground. 2) In testing the truck, I found the 12v battery power isn't getting juice. I'll fix that. But would that even be related?

Try spraying compressed air into the trailer plug that connects into the truck. Then do the same to the truck. I then use electrical grease to keep out dirt and water!! This happen to me several times.

[Funkmoney]

Quote:

Originally Posted by PapaHepcat I had to wire up my truck for pulling a TT (dealer told me it already was, and I was dumb enough not to check). I got it all wired up and everything. Tested it all with a simple tester and everything works in the plug as it should. Problem is, when I test the trailer lights when plugged in, the left turn signal / brake doesn't work. I used a battery and tested the connection at the trailer plug, and the light comes on just fine. So what gives? Everything tests fine on the truck plug. Everything tests fine at the trailer plug. But when together. *Edit: a couple of theories... 1) maybe my ground on the plug wire isn't robust enough for all the wiring? I tapped it to another ground. 2) In testing the truck, I found the 12v battery power isn't getting juice. I'll fix that. But would that even be related?

Let me know if it worked.

[Belgian]

Sometimes the copper pin on the truck plug needs adjusting. If you look at the male pin there is a split down the center of the pin. Take a small screwdriver or knife blade and spead the pin. That will give you a better connection when the trailer and truck plugs are connected. You can also spead all tye pins to ensure you have a good connection.

[Ray,IN]

Poor ground is the vast majority of 12VDC wiring issues. If your truck did not come with a trailer wiring package, using an existing ground wire may cause a problem. This does not seem to be your problem though. I suspect a poor ground at the left rear brake/stop/tail light. Remove the bulb and polish the base with a scotchbrite pad, then roll the pad so you may polish inside the bulb receptacle. If this resolves the problem, remove the bulb again and coat lightly with vaseline to reduce future corrosion.
It that didn't work, check the ground wire all the way to the trailer plug for a break or loose connection.
Just a thought, did you check the bulb for continuity? Sometimes the simple things get lost in the forest.

Did I mention-I hate wiring problems_.