Brake Light...Out of the blue!
 

The other day, I start up the truck. Sure, it has been sitting there for a bit but it cranked right up but out of the blue the Brake Light on the instrument panel comes on. I have checked the master cylinder and there is plenty of brake fluid. So, what gives????? :confused:

With disc/drums it usually means something is out of balance on the pressure between the fronts and rears. Can be a fluid leak or crud in the proportioning valve or master cylinder. Start with a leak check by inspecting the calipers on the front and the wheel cylinders on the rear. Also check all the brake lines.

the ebrake may be setting it off, or the master cylender may be going bad

Yep, pull up on the e-brake pedal to make sure it's not that before you go nuts.

I don't recall that I have ever see the brake light come on in my truck when i set the e-brake. I've never see that light come on except for when i start it. is something wrong with my truck? or where is the swith to turn it on with the e-brake?
Sorry don't mean to intrude on your thread but i figured they were on the same lines.

Nathan

I don't remember there being an electrical switch on the e-brake pedal for the light.

good neither do I

Nathan

ooops! You guys are right, I'm wrong. I musta had a brain fart. :o

Sometimes if you pump your brakes hard the valve will equalize and the light will go out for a moment. I guess it could be crud. I would be looking real hard for fluid leaks.

I know for a fact 71/72 trucks have a switch that will turn the light on..as well as brake problems...they are wired parallel...here's a pic of the switch

I had to go out and triple check but my 72 C20 Super doesn't got it. Nor holes for it.

Nope, mine don't have that parking brake switch either. Rare option or add on?

my 72 doesnt have it either. Sound like the proportioner valve stuck. you'll find out when you try to bleed the brakes.One of the wheels wont get any brake fluid if the valve sticks.got to start with an inspection first.wheel cylinders or a brake line could be the problem.look under the rear end for fluid at the inside wheel rims at the bottom of the rim .

Check this website, scroll 3/4's of the way down, you'll find a way to check your proportioing valve. Also, the shop manual for these trucks spells it out. TJ

http://www.classicperform.com/TechBo...t.htm#testprop