OK, I'm working on my buddy's truck and we have this problem that I don't really understand, hopefully someone here does.

Simply put, the brake lights do not function on this truck. They used to and then one day they just quit.

When the switch on the dash is pulled, all the lights on the truck turn on including the tail lights, but when the brake is depressed the brake lights do not light up.

I've checked the grounds for the lights and they are fine. The problem is that no electricity is getting to them. I looked up the brake light wires in a Haynes Manual, then found the wires on chassis. I've traced them back into the engine compartment where they link into the wiring harness and I have tested them this far. They are stone dead. I have also located them below the dashboard but not tested them there.

We replaced the brake switch and this did not solve the problem.

According to the wiring diagram, the wires should at some point run to the Multi-Function Switch. Would this switch malfunctioning cause the problem I have related above? Where is this switch, and how hard is it to replace?

Additional information: This truck blew it's right head gasket last fall, so we pulled the engine apart down to exposing the cylinders, cleaned it up and put all new seals on it. After putting her back together she functioned perfectly (hell, better than before with all the gunk taken out of parts of the motor). Then all of a sudden this happened a few weeks later... is it possible that we unknowingly did something that eventually caused this problem?

Also, all the fuses are fine. According to the fuse diagram all the lights on the back of the truck run off of fuse 1 (15amp). This fuse is fine, I even went so far as to test it with my multi-meter.

Any help would be appreciated.

Thanks!