My 98 gmc 3500 was stolen the ignition busted up now iv replaced the ignition key and cylinder but wen I start it the security light flashes it started for 2 second and dies and repeat so Iv bought a new harness and switch but there seems to be a difference in the harness the old harness has 3 wires the go from the harness plug to the top side of the steering shaft by the brake now I can't seem to get this unplugged any suggestions

 

Before replacing the harness, perform the security relearn procedure.

Make sure the battery is fully charged.