I have an 89 pickup 4x4, 5psd, 22RE. Recently the break light has been coming on and going off well driving. Break fluid is fine, just had e-brake replaced, along with break lines, fuel lines, sender, tank, head pipe, O2 sensor and EFI fuse. Also if I keep truck in 1st gear and hold clutch down it will stall. And well in neutral and foot on break the idle goes low and back to normal fast... So laundry list of problems, but hopefully can fix.

 

Check your booster:

1. With the engine off pump the pedal until its completely hard. Start the engine and note two things: did the pedal soften at all? Second, after a say 10 seconds of idle does the pedal feel any better.

2. The second thing to check is if vacuum is getting to the booster. There is a plastic check valve on the vacuum line going from the manifold to the booster side. Carefully wiggle/twist the check valve to momentarily break the seal on the hose on the booster side. If you hear a hissing, you are getting vacuum to the booster. If not, check the engine side (probably not a booster problem). Go from there.

If #1 is NO and #2 is YES on the booster side, you have pretty much confirmed your booster is FUBAR.

If brake fluid is fine, its your e-brake switch. There is a switch connected to the e-brake lever under the dash. Probably need to back it off a little.

Check it though:
With ignition on but engine not running, you should have the red brake light on. Pull the e-brake and it should get brighter. You should also be able to hear the switch at the very beginning of the lever travel. My guess is that your switch is partially engaged.

Good luck.