The red Brake warning light turns on for three functions. The parking brake, the low fluid level sensor in the reservoir, and the pressure-differential valve. That valve trips when there's a failure in one of the two hydraulic systems. You can verify that by unplugging the switch. Follow the two steel lines from the master cylinder down to the combination valve on the frame, right below the master cylinder. There will be a single wire plugged into the middle of it.
If unplugging that switch does not make the warning light go off, unplug the level sensor on the master cylinder reservoir. If that makes the light go off, and the fluid is high enough, the float sank causing the switch to turn on. If the fluid really is low, there's either a leak or it's time to have the front brake pads replaced. You can add a little brake fluid but don't fill the reservoir. The fluid will go back up there and overflow when the brake pads are replaced. Be absolutely certain that no petroleum product gets in the brake fluid, not even a film of grease on your fingers.
Wednesday, February 26th, 2014 AT 7:53 AM