780 trailer tail lights not working

check LCM for fault codes first!

 

is it all the trailer tail light or just the outside and center (2 work and 5 don't)

you did check BOTH fuse boxes

 

replace the fuse in the dash (or if it has a relay resettable one replace that with a fuse of the same rating).

But after replacing the fuse check at the pig tail before connecting it again. If you have a short in the trailer plug, or anyplace in the trailer, the dash fuse will blow before the breaker in the trailer plug socket.

 

what lights are working and what lights are not working, truck and trailer, truck and trailer stop,tail turn... running lights truck and trailer... sunvisor...?

did you check BOTH fues boxes....

 

no fuse boxes in trucktor. All lamps are LCM controlled. six fuses of LCM are all of power supply. Any fuse ore bulb goed bad - LCM throws fault codes.

But some trailers, like Schmitz have fuse boxes in rear end of trailer. I'm not sure about all US trailers, becouse I used to tow Mond and Utility and no fuse boxes.

 

our U.S. BUILT volvo has 2 fuse boxes. the lcm will ONLY THROW A CODE if one of the head lights goes out.. NOT for turn/stop/runing/fog/trailer lights and the lcm CAN'T throw a code for the trailer lights it doesn't know how many lights the trailer has so how would it know if 1 went bad...? remenber us trailers have 13 to over 50 lights

 

yeah, but there are current limits for broken circuit to short. So if there is one good bulb in right tailamp - no fault code, if circuit is short = yep, short circuit code, and if all lamps are bad - fault code.

It is not all, new, 2010-2011 trailers got LED tailamps and '03-08 LCMs are not designed for LED and throw codes and keep blinking with LED! I had to disable bulb fault monitoring!!!

 

i have a 06 volvo 780 and pull trailers all the time that have led lights (all our company trailers newer then 2008 have all led's) and NO CODES and the next trailer will not have led's, same thing NO CODES. the trucks lcm doesn't care and never throws codes for trailer lights.

the trailer i had YESTERDAY had a bad turn signal when i hooked up to it and NO CODE, i've had trailers with lights MISSING and no codes. had a blown fuse for the trailer running light and NO CODES...

the ONLY lights on a U.S. BUILT volvo that can't be changed to a led without reprograming the lcm is the head lights, i know because i've changed all the lights on my truck to led's stop/tail/turn/side marker/ day time driving and NO CODES

the lcm doesn't know if 1 light (on the trailer) or all the lights (on the trailer) are burned out,

we are talking about U.S. BUILT volvo's