Check your vacuum switch. Driver side fender right next to the hood hinge. The only time the brake light would come on without the ABS light and aside from the parking brake being set, is when vacuum is low.

 

That's what I'm thinking. Last time that brake lite came on was when my cruise control would not stay on and when I looked at that switch I noticed the hose heading to it had a slight tear. Will check that out too and post findings

 

The brake warning switch (balance valve) and the vacuum switch are wired in parallel. Both can be easily disconnected. Do that, observe that the light is out, then reconnect them one at a time to isolate the problem.

 

J- where is the balance valve located? Another question: you think my pos booster from O'Rileys is going bad after 6 months? I know the FSM calls for a high pedal when the booster goes bad, but isn't that the main source of vacuum that's brake related? My cruise and a/c heater controls all work flawlessly, and those are vac actuated. After I bled my brakes this weekend all worked and now the pedal fades away and that brake light comes on

 

The balance valve is on the inside of the frame on the left side in front of the cab. Follow the brake lines from the master cylinder down.

 

Mark, Ragu has a 93 and I believe that the combination valve (Dodge's words ) is located just below the MC in a much easier to get to location...Mark

 

You can see it here to the left of the starter.

 

OK My bad. Thanks Mark.

 

Is there an electrical connection to the balance valve?

 

Yeah one wire.If I remember right it grounds the circuit to light the bulb.

 

Sometimes a booster will develop a leak that only occurs when operated. You get normal pedal at first, then as the vacuum pump gets behind the pedal hardens up.

Mine turns on the light with low vacuum at a stop light if it's below 0. Otherwise it seemed normal. Lately I notice pedal effort increasing. I think it's time for a booster.

While on the topic, looks like the new last year Chi-com Bendix MC is letting go on one circuit once in awhile, worse when cold. Bummer

 

Booster info from Mysteryman:

NEWS FLASH : Bendix Master Vac Power Brake Booster problem solved

Hi all,
For the last few years I have been working on a solution for the vacuum brake booster failures. In years past it was a rather easy problem to solve. When the booster leaked you replaced it with a NEW booster from Bendix. Ok great. Bendix had plenty of them. . Well Bendix shut down its booster plant in 1992. Again. . . no problem. I bought a bunch of them before all the inventory went away. I did not think I would live long enough to use them all up. . . . Well I have. Again I thought it was no problem. I would just buy a reman. . . . WRONG ! I tried that and the results were some what less than favorable !!!!!!!!!!!!!! I have now put 3 remanned boosters in my 92 flat bed in the past 2 years. . . . This is really pissing me off . I guess I'll have to solve this one also. .
The problem with these boosters is that the rubber parts shrink as they age causing them to leak. Leaking master cylinders also ruin boosters by allowing the brake fluid to leak out out of the back of the cylinder down inside the vacuum chamber.
In the old days I used to rebuild my Midland made boosters. It was easy to do. They came apart with a big v band clamp and a bolt. But the Bendix units such as our trucks use are crimped together. They were throw aways . They were never supposed to be fixed. Hmmmmm. . The aftermarket rebuilds them all the time. . . . How are they getting them apart with out ruining the cans in the process. . . . I have tried every way the rebuilders have recommended but never quite got the results I wanted. . It turns out that the rebuilders violently take them apart . Not exactly what I had in mind. The bottom line is that 1) the rebuilders are mangling the cans during tear down 2) They are NOT replacing the rubber diaphrams most of the time 3) They are mangling the cans again when they recrimp them.

So Last week I started from scratch. I stopped listening to rebuilders and developed a new way to get them apart WITHOUT DAMAGING THE CANS AT ALL !. And it is easy and requires no special tools.
Ok now we have to put them together. . I don't like crimping them. I prefer bolts. So I machined 2 large rings on the lathe. One ring will go on the front can , The other on the back, Then I drilled and tapped the rings to take bolts. . . . Problem solved !

As a side note. The smaller brake booster rebuilders that built good units have pretty much all either stopped doing light truck/ car or gone out of business. There are several reasons for this. The main reason is because of a company that calls themselves A1 Cardone. The other is the overseas competition. The carone boosters are built down in Mexico. (Cheap labor) The booster cores they use are often JUNK and should HAVE been scrapped. They also only replace the rubber parts that they absolutely have to replace. The rest they reuse. . The old rubber parts are washed in a solvent that causes the rubber to slightly swell. This is to be sure that the booster will seal up nicely using the old rubber. Then a few months to a year later the solvent evaporates and the rubber shrinks back . The booster starts leaking and your back buying another one.
Cardone is so cheap that they do not even paint them. They leave them bare steel. To make matters worse they put oil all over them as well as silicone rubber lube over spray on the cans to keep them from rusting. It makes it a real pain in the *** to paint ! The last booster I bought from them for one of our trucks cost me 67. 00. Nobody can build a booster that cheap and do it properly !

My goal is to rebuild a booster properly and inexpensively . I now have all the parts to rebuild them. The parts to rebuild these boosters have never been offered for sale to the retail public. I am going to make a video on how to rebuild them and post it on you tube. I am going to make the parts available to everyone. Stay tuned for more on this . . . ///MM

 

Thnx, Pape. Good stuff. Who is this MM guy anyway? Anyway, the brake light is on always now every time I hit the brake. It's stiff at the bottom, but truck takes forever to slow down. It's as if there's not enough ummph grabbing at the rears. I've read all the steps to perform a vac test in the FSM to check and see if it's the vac pump, booster, etc., but I highly doubt it's the pump. I'm going to bet it's either the entire booster itself or the check valve on the booster. I will check my hose connections too. Man, I'm going to give the reman boosters one more shot, and start planning and obtaining parts for hydroboost brakes. Seems like that's the way to go. Is there anyone that sells a retrofit kit conversion rather than hitting the wrecking yards and obtaining used pieces? Not even sure of the model years to target. I believe I have to source out a different power steering pump also.

 

Have you disconnected the wires I recommended yet?

If disconnecting the balance valve shuts out the light, the MC is bad. (assuming you don't have a puddle of brake fluid somewhere)

If disconnecting the vacuum switch shuts out the light, troubleshoot the vacuum system. disconnect vacuum lines from the master hose one at a time and plug the hose, starting with the most likely culprit, the booster.

Booster faults other than a vacuum leak will not light the lamp.

The quickest and least expensive path to a repair is proper diagnostics.

 

I will in a few. Heard my brakes at the rear squealing bad. I'm guessing they are not releasing once I step on the brake. Sucks man this and the camry are my only forms of transportation and this am the camry battery light on the dash came on and lights were all dim. 2 month old battery too! So I made the choice to drive with bad brakes rather than chance running out of battery and getting stranded