I have a problem with my lights on my trailer that are driving me nuts. On the left rear light the turn signal and brake light work but the taillight doesn't work. On the right rear light none of the lights work. I have no power going to the taillight lead on each side. On the right side I have I have 12 volts coming to the brake light light wire but as soon as I hook it up to the taillight assembly I have less than one volt. So I figure that it must be a ground issue. I find the ground for the rear lights on the frame and give it a nice new clean connection. Still the same thing. I have searched the forum but I couldn't find anything. I would greatly appreciate any help at all.

Check the splices in the junction box if equipped under the tongue of the trailer at the end of the umbilical cord.

The drop to 1V under load means you have a poor connection on either the ground or hot lead. You can test the ground by turning on the brake lights and measuring the voltage on the left light but connecting the negative lead to the ground on the right light using a piece of scrap wire. If you still get 12V both grounds are fine.

I always start debugging this kind of issue at the trailer/truck socket.Get a voltmeter and test each of the pins on the truck first and eliminate that part. The plug the trailer in and test the socket and test each pin.Start moving backwards - you're problem sounds like a bad/corroded connectionsomewhere. I'd bet it's the ground - I had a similar issues and found a loosechassis ground - it was hard to spot but I saw a tiny spark at the junction which gave it away.Gerry

Thank you for your quick response. I will start from the truck socket back and see what I come up with. Thanks again.

I have found the resolution to many grounding issues is to use a STAR washer.

Trailer Light Issue | Good Sam Community

14 Replies

wnjj
Explorer II
Jul 28, 2015
timaford wrote:
I replaced the plug on the trailer an now all of my lights work.

Excellent! Nice work and thanks for updating us.
timaford
Explorer
Jul 27, 2015
I replaced the plug on the trailer an now all of my lights work.
timaford
Explorer
Jul 24, 2015
I believe I have figure out the problem. I cut off the trailer plug on the trailer where it was spliced to the trailer wires and hook it up to my truck and tested for voltage on the leads. On the running lights I was getting no voltage and on the right turn I was getting less than a volt but when tested directly at the truck there was 12 volts. I tried cleaning the trailer plug connector but nothing helped. I am buying a replacement one today on my lunch hour and shall see if that solves the problem tonight.
timaford
Explorer
Jul 23, 2015
There is not a junction box. The wires run all the way to the back of the trailer where they go inside the trailer.
Hornnumb2
Explorer
Jul 23, 2015
Before cutting the plug follow the wire back to the junction box and test there. It should be on the tongue or right near the front of the trailer.
timaford
Explorer
Jul 23, 2015
Well I have made sure that they grounds are good and I still have the same issue. I know that I have power out of the TV. So tonight I will be cutting off the trailer plug and redoing those connections and see what that gets me. Thanks again for everyone's help
RJsfishin
Explorer
Jul 22, 2015
wnjj wrote:
The fact that the left tail light doesn't work when the left brake/turn does says there is more wrong than just a bad ground. The tail light hot lead has a problem too.

Don't bet all your money on that ! I have seen that happen a lot more than once, and its always a ground issue.
enblethen
Nomad
Jul 22, 2015
OP:
A suggestion would be to use a short jumper wire and feed each of the lighting pins on the trailers connector. Using this "known connection will determine whether it is the trailer or the TV. A 314 or so wire connected to the trailer battery then insert into each of the lighting pin position.
Make and model of TV? Some have fuses that control the wiring to the trailer connector.
There could also be problems in the trailer connector.
wnjj
Explorer II
Jul 22, 2015
The fact that the left tail light doesn't work when the left brake/turn does says there is more wrong than just a bad ground. The tail light hot lead has a problem too.
fourthclassC
Explorer
Jul 22, 2015
I have found the resolution to many grounding issues is to use a STAR washer.