I have a 2wd 77 F100 with manual front disc brakes. Replaced all the brakes and bled the system and brakes are working fine. However the brake light comes on and goes off about half the time. Does the valve need centering or resetting? Replace the switch? I unplugged the wire and seems to be working correctly. The entire wiring harness is from a 75 truck, but that shouldn't have anything to do with it. Not sure what to look to fix this. Any idea's?
Thanks, Shane

 

Typically in dual hydraulic system, the brake indicating light will illuminate when the front and rear pressures are outside of a specific differential. This will mean that there is air or something in the system that may not permit the front to rear bias to operate correctly.

You replaced the brakes, and mentioned that you bled the system? Why did you have to bleed the system? Did you replace a brake line or something? There should not be any reasonn why the system would have to be bled unless air was introduced or the closed system has been broken or opened.
That being said, it sounds as though you have a rear set of brakes, or just one side that is not adjusted properly, or you stil have air somewhere.
You can reset, or center the prop valve, but this may not fix the problem that has it off center to begine with.
I believe that you have to figure out why you have such a difference in pressure from front to rear.

 

The truck had no rear brakes at all. I had to replace one line and both wheel cylinders. The front brakes were ground right into the rotors so I machined and installed good rotors and pads off a parts truck I bought. Bleeding took quite a while. Maybe it just has to be bled again? Brakes are working real good, but the light is on sometimes.

 

Make sure the rear shoes are adjusted properly to the drums, then bleed system again.

 

The warning plug may be cracked, allowing brake fluid to seep, setting off the light.