I did the kind of bypass you are asking about to a 96 camaro which is passkey II and I believe would be same/similar. In the camaro, the 50Hz signal you are talking about is sent from the BCM to the ECU (PCM). The BCM is a separate box and on the camaro is located inside the passenger area. But the wire that you have to cut and feed the circuit into is one that goes into the ECU/PCM.
I believe this is a dark blue wire and is called the "Pass key fuel enable" circuit on GM schematics. For the camaro it is circuit 55. Good luck - hope this helps.
