Bosch Voltage Regulator saved the day!
 

I had my 986S up at Road America for a volunteer event last Monday and the dreaded battery light game on as I pulled into Elkhart Lake, WI. After the event (I was a corner worker), a nice guy with a trailer offered to check the voltage with a multimeter, then a bunch of other guys came over to offer assistance. We started up the car and sure enough, voltage was not increasing, so one guy gave me a battery charger so I could make it back to my storage facility in Hartford, WI.

I made it without incident and ordered a Bosch voltage regulator from ECS Tuning, as suggested by a number of threads on Rennlist.

A bit of a pain to get the alternator out, but all went well and the battery light is off. The new regulator was $50 and I am grateful for the awesome information sharing on this site and also for the kindness of car folks up at Road America.

Looks like the old voltage regulator is a knock-off version. In the receipts I have from the PO, the alternator was replaced 4 years ago, but I question this as the alternator looks original and the pulley is rusty.

Enjoy Independence Day!