Tail lights?

Thread starter #1

Flash

Senior Member
Trailer, flat four connection, one tail light won't work. blinker fine, it's not the bulb. What's the most logical thing to look, try next?? The flat connector from the trailer?? Other trailers no problem Thanks
 

Deerhead

Senior Member
If all the recommendations above doesn't work replace with LED. Harbor Freight has some at a reasonable price... I keep extra lights on hand just in case.
 

Gator89

Senior Member
On my trailer both tail lights stopped working, but brake lights and turn signals worked. All wiring tested good. Problem was a blown fuse.

If only one tail light works, use a meter to check continuity, ground, etc.
 

baddave

Senior Member
you sure it's not the bulb?? those bulbs have 2 separate filaments ,the blinker and running lights are different. Just look at the filaments.
 
Had the exact problem recently. Changed out the trailer pig tail, good to go. All lights worked on a trailer that had set for 5 years. Problem lives on the trailer.
 

Spotlite

Senior Member
I ended up having to replace the tail light on a trailer recently. Couldn’t get brake light to work. It was a bad connection in the socket somewhere. Kept tinkering with it, work one day, not the next and for $24 bought a new set.
 
Thread starter #15

Flash

Senior Member
If it's the ground why would the blinker work and not the tail light?

I tried different bulb, same thing. I might have another pig tail to swap out and try that .
 

notnksnemor

The Great and Powerful Oz
If it's wired correctly and one tail light works and the other side doesn't, check continuity in the brown wire going down that side of the trailer.

This should help:

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To be sure of a good ground connect your jumper cables from frame to trailer ...
None of the lights would work if there was no ground. System ground would not be selective on one light only but socket ground could cause one to not work but both filaments in that socket should be affected equally.
Need to take a test light and see if you have power to both contacts in the socket...one should be continuous when the tail lights are turned on and the other should flash when the signal is on. Sounds like the brown wire is likely open to that socket.
 

jimbo4116

Un-Retired Moderator
Staff member
None of the lights would work if there was no ground. System ground would not be selective on one light only but socket ground could cause one to not work but both filaments in that socket should be affected equally.
Need to take a test light and see if you have power to both contacts in the socket...one should be continuous when the tail lights are turned on and the other should flash when the signal is on. Sounds like the brown wire is likely open to that socket.
Most trailer light fixtures are grounded directly to the trailer frame at the fixture, not by cable back to connector plug. You can have a bad ground on one fixture.

That said, I have had a turn signal or brake light not working and used the old penny trick on the trailer ball and they start working. I can't explain that but it does sometimes work.

One of the testers mentioned above will tell you if you have problem with the wires from the plug back to the trailer or forward in the truck, such as a fuse. Most trucks now days have separate fuses for trailer lights and truck lights.
 
None of the lights would work if there was no ground. System ground would not be selective on one light only but socket ground could cause one to not work but both filaments in that socket should be affected equally.
Need to take a test light and see if you have power to both contacts in the socket...one should be continuous when the tail lights are turned on and the other should flash when the signal is on. Sounds like the brown wire is likely open to that socket.
That is not totally true ....I have seen it that sometimes they will back feed through another light to have a ground ....

I have solved some trailer problems by finding that my ground was not a good ground ....
 
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