Brake warning light help.

[derotoreut]

I am trying to figure out why my brake warning light won't work. I understand it should come on when the truck is in the "On" or "Start" position, and go off when running (as long as there are no leaks or differential pressure in the system). When I turn the key it won't come on at all.

I have a new Painless wiring harness installed. I tested the warning light by putting a 12V power source to the wire at the proportioning (combination) valve and it does light up on the dash.

Sounds like the problem might be the switch at the prop valve. Does this sound right or should I be looking at something else?