Ford Repair: in dash brake light, smooth jaw, proportioning valve

Question

 Hey Jeff,

 wanted to know what makes the in dash brake light come on in my 79 F150... i know the parking brake will turn it on, and that is not what is keeping my light from intermittently coming on... front pads are new and (in desperation put a smooth jaw locking plier on the rear brake line to the rear end) have bleed the system. but pedal is still low and light is on and off.  i know the proportioning valve makes my light come on, but why... is pressure not equal or is valve bad...is my master cyclinder on building proper pressure...
 just wanted to know if you could help...
    Thanks   Thomas

Answer
Hi Thomas,
The only other thing that can turn the brake light on is the fluid level switch in the master cylinder. Make sure the fluid is at the correct level and that the float is not stuck down. If all OK, change prop valve. It is probably sticking. Then bleed brakes again. GOOD LUCK!

Jeff
AllExperts