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

timaford
Explorer
Jul 22, 2015
Thank you for your quick response. I will start from the truck socket back and see what I come up with. Thanks again.
fitznj
Explorer
Jul 22, 2015
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 connection
somewhere. I'd bet it's the ground - I had a similar issues and found a loose
chassis ground - it was hard to spot but I saw a tiny spark at the junction which gave it away.

Gerry
wnjj
Explorer II
Jul 21, 2015
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.
enblethen
Nomad
Jul 21, 2015
Check the splices in the junction box if equipped under the tongue of the trailer at the end of the umbilical cord.

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Trailer Light Issue

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