About a week ago the brake light on the cluster turned on and will not turn off. Brake fluid has been topped off and there is no continuity when testing the terminals on the side of the master cylinder reservoir. The parking brake switch under the console is functioning properly. All three brake lights are also working.

What could it be? I have an appointment to get the master cylinder replaced but I am questioning if that is the problem being that there is no continuity between the terminals on the side of the reservoir when filled to MAX. Is there anything else I can check before dropping a few hundred?

The car is meticulously maintained and is not daily driven. It has about 71,000 miles.

 

If your alternator is going bad it can cause this issue. Just from the car sensing no output it'll do this. Check your alt and report back.

 

check ur brake resoivor for the white thingy. it might be stuck at the bottom. use something to poke it n see if it will float up.

 

^ This. You say you topped off the fluid. This means it was down? Sometimes when the brake fluid level goes down and you top it off, the float gets stuck in the low position. It has to be "unstuck" or it will constantly see "low" fluid.
Next, you gotta ask why the fluid got so low. Is there a leak? Are the brake pads worn too thin?

 

If the pads are worn down thin and you topped it off, be sure to monitor the level as you depress the caliper pistons when replacing the pads. You wouldn't want it to overflow.

 

Pads were replaced about 10,000 miles ago. Brake fluid was well above the MIN line when I topped it off.

 

I once had a piece of paper slip through a seam and into the console and interfere with the parking brake switch so the light stayed on.

 

Have you checked your alternator as I suggested? How much have you driven the vehicle with it on?

 

Alternator is good. Car has been driven about 30 miles since the light came on.

 

Try adjusting your parking brake. Should be 9-13 clicks. This warning light is a very basic circuit. 2 inputs; reservoir level and e-brake. You already checked the lack of continuity so power can only be coming from one other place. You indicated the brake was ok but most likely only did the switch test from the connector to ground. Most likely an e-brake issue adjustment issue.
Remove center console and loosen the e brake nut in the rear console opening completely. Pump your brakes several toms to set the self adjustment. Raise rear of car and raise brake lever 1 click. Tighten adjusting nut with a friend turning the rear wheel until the brakes just start to drag. Release lever and verify wheels no longer drag when turned. Lower car and pull brake lever. It should be 9-13 clicks. If that doesn't work you need to access the caliper, screw in the piston "+" , align the tits on the pads to the slots and repeat the adjustment.
Utah