Haven't owned a MKIII for a couple years and haven't worked on one for several months. If I end up working on one anytime soon I'll try to get you a photo.
http://www.cygnusx1.net/Supra/Librar...spx?F=8401&P=4
http://www.cygnusx1.net/Supra/Librar...x?S=Main&P=136
If it is the parking brake switch pressing it will open the circuit (no continuity) and releasing the plunger will close the circuit (you'll have continuity). If you have the key in the ignition and turned to the "ON" position the "BRAKE" light should light up when the plunger is released. If you do not see this indicator either case then try replacing the bulb. If this light it always on then test the switch to make sure it's operating correctly with a multimeter and then diagnose the brake fluid level sensor in the brake fluid reservoir.