my trailer left turn signal and brake light stopped working.
The running lights work on the trailer
The lights all work on the truck.

I am hooked up to a 2007 F150 and it all worked 'yesterday.' not sure where to start.

 

turn and brake are the same filament in the bulb.. If the other side works and running lights work, my first guess would be the left bulb.

 

also look at the 10 amp fuse #42 in the elect box on left fender well.... under hood.

 

I have the same problem, but the right side isn't work( brake light and turn signal.) I replaced the bulb with a new one, and replaced the fuse #36. ( my truck is a 2004) Is there any suggestions to either of our questions. I'm starting to think it is a grounding problem, but i don't know how to locate and fix it, if it is the problem, haha

 

Please see your other thread, do not post the same thing multiple times.

 

ford1999 ------ your problem is on the TRUCK lights... the original post here concerns the TRAILER feed.
------------ and F150, I said the elect fuse box was on the fenderwell... it should be the one under the dash/ steering wheel.

 

Any chance there's an issue with the trailer wiring?