I have an 04 Silverado 2500HD with the Duramax and am pulling a very small
trailer with camping gear. A buddy (following me) tells me that the left
brake light on the trailer doesn't work. He also tells me that the left
and right turn signals work and that the tail lights work. So: The bulb
is a double filament and both filaments light when they get power. The
bulb is good. The connecting wire is also good since both circuits light.
The trailer has a flat-4 connector which is plugged into the truck 7-pin
receptacle using the Chevy-supplied 7 to 4 adapter. Tried another one
adapter with the same result.
It seems to me that there must be a separate trailer brake light circuit in
the truck, maybe with it's own set of circuit breakers, fuses, and
Any suggestions? Other than take it to the shop?