Brake Light.
 

I am going to assume the brake light on the instrument panel just indicates that the parking brake is on, I can't imagine that there are sensors for the brake system indicating there is a problem. The reason for me asking this is; I was driving in to work today and noticed the brake light was on (parking brake was off), the brakes work fine, so I am guessing it is just the switch for the parking brake that went bad. If some one can let me know if the light means something more then what I think, I would appreciate it.

Thanks,
Josh.

Re: Brake Light.
 

Brake light means there is something wrong. Check the fluid level in the MC, check for leaks in the whole system. Though it could be an electrical malfunction.

Re: Brake Light.
 

I will check the fluid level.
Thanks

Re: Brake Light.
 

If your truck has a brake proportioning/combination valve: there could be electrical content there. If you have a leak in the front half or back half of the system, it will "shuttle the valve" to close the offending side off - and - turn the light on in the dash.

Because most of the braking is done with the front, conceivably you could close the rear brake system off and not really even notice.

K

Re: Brake Light.
 

I will give that a look as well.
Thanks

Re: Brake Light.
 

If the tan wire going to the prop valve is shorted to ground it will also cause the light to come on, a quick test is to disconnect it from the prop valve if light stays on problem is in the wiring if light goes out problem is in the brake system

Re: Brake Light.
 

On factory dual/split systems, which I think is everything since 1967, there is a switch in the distribution block. This switch will light the brake warning lamp in the event of pressure loss on either side of the system. Unfortunately, it doesn't reset automatically. Disconnect the wire from the switch, and if the lamp goes out, that's where the problem is.

Ray

Re: Brake Light.
 

If the problem turns out to be the Proportioning Valve, is it safe to drive it for short distances till I get time to fix it? The last thing I want is to lose my brakes and wreak my truck.

Re: Brake Light.
 

Ray,
Are you talking about the the wire that plugs into the Valve body?

Re: Brake Light.
 

I only got this truck about a year ago and I don't know what kind of brake fluid the previous owner might have used, I am guessing DOT 3 is standard for these trucks, am I correct?

Re: Brake Light.
 

DOT 3 brake fluid, IIRC. The wire goes to the proportioning valve which connects to the master cylinder. I would figure this out before you go driving around.

Re: Brake Light.
 

Yes, that's the switch. Just disconnect the wire and see if the light goes out.

Ray

Re: Brake Light.
 

I think I found the problem, after looking in the engine compartment, I noticed brake fluid that had leaked onto my firewall, look at the MC and found that fluid was leaking out of the top from the rear reservoir. I took the cover off to inspect the gasket and noticed some dirt on it as well as on the top part of the MC, I cleaned them, filled up the rear reservoir and no more light.

Just want to thank everyone for the help.
Josh.

Re: Brake Light.
 

Glad you got it sorted out. I would keep an eye on it just to make sure.

Re: Brake Light.
 

I will keep an eye on it. One question, would a bad seal on the back reservoir cause the brake light to come on, would that create low pressure for the back brakes? Well I guess thats two questions.

Thanks again,
Josh

Re: Brake Light.
 

Low pressure for the back brakes would cause the combination valve to "shuttle" (ie, shift off center) turning on the light.

Hopefully, adding fluid restores the pressure to the rear, and the first "hard" depression of the brake pedal re-centers the combination valve, turning the light back off.

That's how it's supposed to work, anyway -

K

Re: Brake Light.
 

If the seal was bad and it was leaking, yes.

Re: Brake Light.
 

That is exactly what happened, filled the fluid cleaned the gasket and when I came to a hard stop I felt a little click or something on the brake pedal and the light went off. I am glad it was an easy fix; I was getting ready to get a new Proportioning Valve and heard that it can be a pain to get the new one working properly.

Josh

Re: Brake Light.
 

Going back to your original post, I don't think the dash light serves two purposes. It doesn't indicate when the parking brake is on, it only indicates trouble with the braking system.

Re: Brake Light.
 

I am experiencing a similar problem, except my brake light on the dash is flashing. It's never done this before, and everything appears to be okay. I checked the brake fluid, and the truck stops fine. The weird thing is that it also flashes when the ignition is on, but the truck is off. . .

Re: Brake Light.
 

Isn't there a brake light switch on the parking brake? Or am I thinking of my Chevelles?

Re: Brake Light.
 

I think your right, I thought it came on with the parking brake, but now that the problem is fixed the light dose not come on with the parking brake engaged.

Re: Brake Light.
 

Does anyone have any thoughts about why the light would flash??

Re: Brake Light.
 

Dose it flash all the time?

I would not know why it would flash, but try unplugging the wire on the valve body and see if you still have the problem, if you do its electrical and not mechanical.

Re: Brake Light.
 

Do the test in post #6 if the light doesn't go out or stop flashing then that means the tan wire is shorting to ground. the tan wire also goes to the ignition switch to illuminate the light while cranking to serve as a bulb check.