A bit of dielectric grease on the grounds keeps them from corroding, a must in high humidity climates.

Follow up the ground repairs with a look at the bundle of red wires attached to the positive battery clamp. I find many of them loose under the 6mm nut, and they power the ingition switch and light switch.

Excellent point. I did mine. I don’t have a non shiny point on the car now. Runs great.

Yup. Fluid Film can be used as well. Easier to spray, and useful for other rust-proofing.

A lot is just simple cleaning after no one has for 30 years. Always kills me how many cars have never been sorted. Bushings, seals and grounds are like basement floors, a good roof, and decent plumbing.

I see so many unsorted cars.

I found this post interesting since my 77 911S just started shutting off while I was driving, as if the ignition key turned off. I turned on the key all the way right and it started right up while rolling, ran fine and did this again a mile later. First thing I thought of was the battery cables. Gonna first check the three ground cables mentioned above.
One question, is the alternator to engine ground cable the same one that the spark plug wires are grounded to (a nut on the timing chain case) ?
Thanks
Tony

I can’t speak directly for an S but on a 3.2 it’s one small brown wire that I replaced with a 1awg that goes FOM the Alt Ground to the top of the bolts on the case.

Check and see the part manual for your car. Porsche classic online has it. I know something grounds to the fan shroud on an SC..

No, there is a main ground wire from the alternator to an engine case bolt under the shroud. Spark plug wire shielding is not part of it.
Coil negative to ground is much more important than the shielding. It goes to the base of the coil mounting bracket.