3850FL Reverse/backup lights not working

[napria]

All our lights are working on our truck and the Monty, except the Monty's reverse/backup lights. Any suggestions on how to troubleshoot? Will messing with the wiring in the pin box void the warranty?

[jfaberna]

I bought a little tester for $20 that plugs into the truck socket and test all functions. That would at least let you know it's absolutely a trailer issue.

[jfaberna]

Another thing. When I got my trailer umbilical cord ripped off, the mobile tech who replaced it asked if my trailer had backup lights. Apparently some trailers do not. So he made sure to wire them to the new cable and check them. Not sure what that tells you, but in the wiring box at the king pin box there is access to all the trailer navigation lights.

[napria]

We figured out the backup lights, but now the right turn signal/brake light won't work. That tester sounds great. We'll look for one.

[BB_TX]

Go to this etrailer.com site and scroll down to the 7 way trailer connector diagrams.
You can use a jumper wire to jumper pin 4 (battery +12v) to what ever pin corresponds to the lights you want to check. That will test your trailer wiring.
Just don't jumper pin 4 to pin 1 (ground).

[bethandkevin]

You don't say what year your 3500HD is. Newer models have fuses in the underhood fuse block for the trailer lamp functions. Also, the trailer connector on the truck has a connector that plugs into the body. That is a common area for corrosion.

[napria]

quote:Originally posted by BethandKevin

You don't say what year your 3500HD is. Newer models have fuses in the underhood fuse block for the trailer lamp functions. Also, the trailer connector on the truck has a connector that plugs into the body. That is a common area for corrosion.

Ah! When I updated my signature the truck year was lost. Or I never posted it to begin with. It's a 2004. The fuse box is by the drivers side door in the dash. We've replaced all the fuses. That fixed the backup light problem, but we still have non-functioning right turn signals.

[bethandkevin]

I just looked up the schematic. That circuit runs through a 10 pin connector underneath the fuse box under the hood. Past that there are no connectors until the actual trailer plug. In that its a dark green wire at pin "D". The wire is dark green the whole way front to back. Used to see "critter damage" under that fuse block.

[napria]

Thanks. My husband has gone to look now.

[Loui]

Some fuses for the trailer lights are where you found them, drivers side door, but there are some under the hood in that fuse block as well.
I don't know why GM wouldn't put all the trailer related circuits in one area
so check the fuse box under the hood as well