^^Thanks for the great advice and DIY! Definitely going in the file for future reference.
Check out this ad I found in Car and Driver from 1987:
M5 Hettel 100.pdf
Yep, that's what I got right there:
I also found remnants of an old HOFCO car alarm:
I checked and the black box has been removed.
" If you were around in the late 70's and 80's then you know these alarms and the patented Hofco passive kill switch saved many Porsche owners from having their cars pinched. It was very common to have stripped out 930's show up on fire in vacant lots around LA and OC, nothing left but the tub. They are inherently easy to steal but putting a small hurdle between the thief and a running engine worked most of the time. Sometimes insurance companies required anti-theft devices before they would provide coverage. The Hofco installation was very sanitary and could be removed without harming factory wiring, ask technicians from that era and they will verify this important detail. There were lots of hacks but Hofco was the only dealer installed alarm system in the LA area from the late 70's through the 80's."
Since the car has a title history starting in California I'm gonna bet she lived some of her early days in the greater LA area. Somebody surely didn't want his baby getting boosted!