Pass-Lock was GM's proprietary anti-theft system, and it's known to be riddled with issues. So, if you need to bypass a faulty Passlock system, you'll need to understand its wiring diagram. First, disassemble the steering column, and find a 3-wire ribbon cable, with the colors white, black, and yellow. You can then turn the ignition key to the RUN position (not starting your car). Strip a portion of the yellow wire, contact it with exposed copper on the black wire, and measure the resistance going through them.