[Trackrash]

That switch on the dash could be for any number of things. Most likely fog lights.

Post a picture of the switch.

These older cars were problematic with respect to the wiring, due to the fact of so many options. I spent something like a week going through my car's wiring back when I did my resto. I ended up with a large box of unused wire when I was done. My car had the harness for the gas heater, which I removed. The issue is that Porsche duplicated wire colors for some of the optional equipment on these cars, making it confusing to follow some of the circuits.

Depending on your sound system, you could connect directly to the fuse panel or even the battery.