I have a F350 box truck truck that is driving me crazy,cant get the brake lights working.This is an 03 gasoline truck with a 165k on it that is worked in some very tough conditions,I chose to keep this truck when my company offered me a brand new Sprinter.I have replaced the brake light switch,cleaned every ground I could find and still have no lights.My signals,tail lamps and backup lamps all work.I was told the combo switch could be the cause but I wanted to be sure before I shell a hundred bucks out.If anybody has a fuse and relay diagram that would also be a great help.I have to travel 90 miles to get any service or parts for this truck so most work is done at home.I am not an electrician,just a very stupid caterpillar mechanic...

 

At motorcraft's website, go to service and then owner's guides. You can download your owner's manuals, the fuse locations should be in there.

I'd check fuses then the brake switch above the pedal before suspecting anyother parts.