To disable a GM passlock, first determine if the ignition is linked to the steering column or next to the radio on the dash and remove the appropriate panels. Search for three bundled wires grouped into either red, white, yellow and black or yellow, orange, black, red and white groups. Find the pass lock two wires jetting from the ignition, and observe pin A6, the yellow wire, and pin B6, the black wire.
Take a small amount of insulation from the black wire, but do not cut it. Instead, cut the yellow wire and strip both ends. Use a digital ohm meter with the negative probe against the stripped black wire and the positive probe on the piece of the yellow wire still connected to the ignition. Turn the ignition to the run position, and note the ohm reading; this translates to the resistance needed to turn off the passlock. Turn the car back off.
Attach the resistor to both the black wire and the yellow wire that feeds into the computer. Cover the yellow wire leading to the ignition with black electrical tape. The car should successfully start if the resistance is matched, and then you can tape the wires and re-assemble the dash. If it does not start, turn off the car and try to start the engine again, and then move it back to the run position. Find the security light on the dashboard, and wait 10 minutes until it turns off, then turn off the ignition and wait for approximately five seconds; the car is now equipped to learn a new password the next time the ignition is run.