2000 Prizm Chevrolet Models Brake I/P Warning Light

2000 Chevrolet Prizm, the brake warning light comes on and stays on until I apply the brakes, the light goes out and then comes back on a short time later. The Chevrolet dealer in our area inspected the brake system, there was 70% pad left in the front and 50% in the rear. Brake function is normal and the fluid level is correct. The Prizm does not have ABS. The dealer said he thought the e-brake lever swith was the problem, I disconnected the switch wire and closed the circuit manually and retested the the vehicle. This did not correct the problem. Can you help? Thanks Steve

Update, this appears to happen during cold wet weather, I took my son to school this morning 21 degrees and the car did the same thing both ways. This afternoon the temp is 42 degrees, I drove the car about 40 miles and did four restarts during the trip and the light never came on once on the afternoon trips. I think the only sensors on the brake system are the switch on the e/brake handle and the fluid level sensor on the master cylinder.