The fuse blows as soon as I tap the brake pedal. I've checked the wiring all the way back and can't find any problems. I disconnected the harness at the back of the truck where the tail light assemblies plug into the harness to rule out any problems with the tail light assemblies themselves. I put a new brake light switch on the brake pedal and the fuse is still blowing. Any ideas on what else I can check?

 

Did youpull check thethe wiring for- the 3rd brake light?
Also, are you positive that the wiring for the brake light switch is ok?

 

Haven't checked the third brake light. I actually didn't inspect the wiring going into the switch so I'll do that too.