Trailer brake lights continuously on

Just unplug the wire under the trailer where the air lines hang down near the sliding tandems. That will cut the power the the ABS "brain" that located in the sub frame of the trailer. If the stop lights go out the "brain" has a short in it. You can run it unplugged safley you just won't have the ABS working on the trailer. This happened on my trailer a couple of years ago and it was about a $750 fix.

 

Yes, as the other posts mentioned, sounds like something is wrong with the ABS circuit on that truck. The center pin from the cord will have power with key on. You could have a short between the center pin and brake light pin, which is the bottom pin I think. Try a different cord if you have one.