A bit late now...… But l believe (on my facelift anyway) that the yellow unplugged cable is the auto arm function. When plugged together the alarm will self arm after a few minuets.

The alarm on ebay is for a '92 build year and may fit yours. Before you rip it all out have you tried programing the remote to the system.??

 

Hi Malc4d, I've of course tried to put plug back the yellow cable before removing everything and I got the same issues, blinking side marker, engine not starting, etc...