Truck Repair: 1988 Chevy truck - brake light stays on, brake master cylinder, chevy c1500

Question
Thanks.  I'll try that.  Is the "wire from the rear wheel antilock module" the same as what I called "the wire on the brake master cylinder"?  There is a single wire with a female plug on it that's plugged onto a nipple on the top of the master cylinder - either on the front master cylinder or rear master cylinder, I don't know which.  Mounted beside the master cylinder is some sort of module that has a plug with several wires going into it.  Should I instead be disconnecting this plug, or should I disconnect this plug as well as the wire on top of the master cylinder?  Where is the RWAL fuse?  Is it in the fuse panel on the bottom of the dash, just below the steering column, or is it on the relay panel up under the dash on the firewall?  Thanks again.

chris

Followup To
Question -
The brake light on my 1988 Chevy C1500 truck is stuck on. It dims slightly when I release the parking brake, but it stays on.  The parking brake works fine, and the brakes work fine.  I checked the brake fluid, and it was not low, but I went ahead and topped it off anyway.  I disconnected the wire from the switch on the parking brake, and I disconnected the wire on the brake master cylinder, and the light still stays on.  I also tried shaking the wires in the wiring harness to see if there might be a short, but still no luck.  The truck has a little over 96,000 miles on it.  This problem just started recently.  Thanks for taking the time to evaluate this.
Answer -
The truck may need to have the brakes bled.
Then unhook the wire from the rear wheel antilock module for a few seconds. Remove the RWAL fuse for the same time.
That should erase a code that could have been set during a hard brake application.

Van

Answer
I believe I unhooked both the wire, and the connector. That is the RWAL module.
The fuse should be marked RWAL, but look in the owners manual, and it will say which powers RWAL.
For good measure, unhook the battery also.
There is also a proportioning valve, that has a switch built in, where a plunger shifts toward the end that has lower pressure, for whatever reason, such as a blown line or wheel cylinder, but a bad master cylinder, and a plugged flex hose could also do it.
The way to reset that switch is to bleed either the front, or the rear, until the light goes out.
To tell if that switch is the cause, find that valve,,,,about 5 or 6 lines going to it, and a wire to a switch. Unhook the wire, and see if the light goes out.

Van
Van