After we did the throwout bearing, I hooked the parking brake cable back up. I did the reverse technique to adjust the rear brakes because the parking brake wasn’t holding very strong, and then I drove it 100 miles back home. Now when I push the brake pedal moderately hard, like for a typical stop at a stop sign, the brake light on the dash comes on and stays on until I tap the brake pedal once or twice. Then it comes back on at the next stop. Fluid reservoir is full. Any ideas on what to check next? I didn’t have any problem until we worked on it this weekend.
I'm not too familiar with the earlier model trucks. Most of what I know is just what I learn from the service manuals/wiring diagrams - so consider the source when reading the following.
From what I can see (in model year 1978), it doesn't look like the e-brake had a switch that could cause the e-brake warning light to come on. Up till that year, the warning light could only be illuminated by the switch in the BPC valve. It looks like 1979 was the first year that an "e-brake applied" switch was incorporated into the circuit.
Should be easy enough to check whether I'm "shootin' it out my ass". Just get under the dash and look up at the e-brake engaging mechanism. If you see a switch with a wire (should be TAN if it exists), then I'm wrong. If you don't see a switch/wire, the problem is with the BPC valve.
From what I read above, the job you recently did (changing the throwout bearing) shouldn't have had any effect on the BPC valve - or any part of the hydraulic braking system. Also, if - and that's a big if - there is no e-brake warning switch, unhooking/rehooking the parking brake cable couldn't cause the warning light to start coming on.
Take the BPC valve switch out of the equation by pulling the TAN/WHT lead off the switch terminal. If that stops the warning light from coming on, there is something going on with the BPC valve.
