2003 Chevrolet Tracker, brake warning light on dash stays on. If the hand brake is applied the light is slightly brighter. When hand brake is released, the light dims slightly. I have checked fluid level and disconnected the two wire connector to the master cylinder. Nothing gets the light to turn off. The pads and shoes were inspected, and look good.
From what you describe it sounds like the warning light is a relatively simple circuit. I'd guess that it is "active low" with the various switches/sensors providing a ground for the warning light. That would explain why putting on the hand brake makes the light a bit brighter – it adds another path to ground and increases the current through the bulb.
So, the first thing to do is to check your owner manual to find out what the light means – in other words to identify the conditions under which it is supposed to be on. It sounds like you've checked some of the obvious problems, but it would still be good to know if there is anything else that could cause the light to come on.
With that list in hand you can check anything that you haven't already checked and then you'll have a good idea if the problem is a fault in the warning light circuit or a legitimate warning.
It would also be a good idea to find out if the circuit is optimistic (no problems unless something signals that there is one) or pessimistic (unless everything checks out ok, there's a problem). An optimistic circuit will typically be built of normally open (off) switches that turn on when there is a problem. A pessimistic circuit would be designed with normally closed (on) switches that are set up so they are turned off when things are ok (for example a float switch in the brake fluid reservoir that is on (makes contact) when the fluid is low and off when the fluid raises the float level).
If none of the switches/sensors are activated, then my suggestion would be to start looking for places were the wires have been damaged and are shorted to ground.
On that year Tracker the brake indicator light is a normally open circuit that's always hot. The light will come on if the Daytime Running Lamps module sends a ground when the parking brake is applied, if the brake fluid level switch closes or if the ignition switch is in the start position.
Remove the instrument cluster and gain access to the 10 pin connector. Backprobe pin 6 (purple - DRL), pin 7 (red/black - level switch) and pin 8 (purple/red - ign switch). Voltage drop each pin in turn (key on engine off or running) and it'll point you to where the problem is. If you unpin pins 6-8 and the light remains on suspect a short to ground inside the cluster it self.