Trailer Light Problem

trees132 · Sep 30, 2013

Hey Guys,

Have a question about an equipment trailer. One of the tail lights works with running lights but does not function for signal and brake functions. Any thoughts on how to troubleshoot this problem? I have a multimeter and can use it a bit.

Thanks!

nikdfish · Sep 30, 2013

Check for voltage on the appropriate wire (green for right yellow for left) while the brake is held or with a battery supplying power to it at the plug, checking at the point the wire enters the light. If power is found & the bulb tests ok then probably a bad socket or bad connection between wire at the point it conects to the light. I have seen a few "push in" connections go bad due to corrosion on wire or light fixture.

Nick

tthopskin@yahoo.ca · Sep 30, 2013

some cars trucks run with 2 different lights now and if you dont have the box .then you need 2 sets of lights on each side one for brake and stop one for turn ...this may be your problem

Diamondpilot · Sep 30, 2013

Should be a two element bulb. Sounds like a bad bulb would be my first guess.

Chris

timswi · Sep 30, 2013

Diamondpilot said:
Should be a two element bulb. Sounds like a bad bulb would be my first guess.

Chris

That would be my first check as well...

Depmandog · Sep 30, 2013

I would guess that over 50% of my trailer lighting problems have stemmed from a lack of a good ground back to the towing vehicles battery. Make sure the trailer is attached to the towing vehicle and your ball isn't rusted and it's properly lubed.

Not suggesting that's your problem..only that's my first order of business when I go to troubleshoot trailer wiring.

aczlan · Sep 30, 2013

timswi said:
That would be my first check as well...

Same here.

Aaron Z

bcp · Sep 30, 2013

And if you have a hitch receiver, the insert may not be making a good ground with the receiver due to rust or paint. I like to see a wiring ground on trailers.

Bruce

BigE_ · Sep 30, 2013

After the ground check and the bulb check, I pull out the meter and make sure I'm getting signal at the bulb. If there, then I go back to the truck and make sure I have signal at the connector.

Lots of times it is the connector itself, especially the 7 pin connectors.

If no signal at the connector, check your fuses. In my truck I have a fuse for each light.

The last wiring problem I had was that both tail lights blinked at the same time when the right blinker was on, but only the left when the left blinker was on. Pulled apart both lights and even replaced some with LEDs. Drove me nuts until I checked at the connector. Same issue at the connector with the trailer disconnected. It turns out that my Silverado has a trailer wiring module. I pulled that out after taking apart the dash. $35 for a new one, so I tore that apart and found one relay had welded shut. Popped it open and good as new.