Expert: Mike Evans - 9/1/2010

Question
i have a 99 gmc suburban and im having a problem with my brake lights. my brakes lights on bottom will not work but the brake bar at the top will checked bulbs and they were fine? now i have no idea what it is, can you help me please?


Answer
    That bulb also serves as the turn signal and tail light bulb.  If you have a trailer hitch, the wiring for the trailer lights goes through a converter that lets the old-fashioned lights on the trailer work.  The first thing I would do is disconnect the trailer lighting harness (there should be a simple plug under the truck on the driver's side at the rear), plug it back together without the adapter, and see if that does it.  If it does, then buy a new adapter, they can't be fixed.  If it doesn't, then a wire has been severed somehow between the taillight assembly and the turn signal switch (the brake lights go through the turn signal switch, but not the high-mount stop light).  Finding the fault will be a matter of tracing the wire and looking for an actual physical break in the wire.