Alternator or Voltage Regulator Problem?
 

I recently noticed that my headlights would brighten slightly when I revved up from idle. I put a multimeter on it and found
13.6V at idle
12.9V with lights, AC and heater blowers running
12.9V at the Optima Red top when the car is off.
While at idle again, out of nowhere, it went to 14.5 then 15 then 16V for a split second and returned to 13.6 and stayed there. :eek:
I drove home and have seen no variance of brightness in headlights (with or without other accessories). :confused:

So, is this an alternator, VR, or both? If VR, can I replace just the VR (I think it is internal on my `87)

Not an expert on this but the sudden changes and spikes of voltage sounds like the regulator. Experts here will confirm or correct.

Its the regulator.

Be carefull not to damage electrical components, dont drive the car before you repair that.;)

the best way to find out is to do a load test on the battery and charging system. i believe some auto stores will do it for free. it's a simple test so they can't really mess it up.

how many miles on the car? could be regulator. replacing the regulator internal type also replaces the brushes.

I had the exact same symptoms in my 88 at 60,000 miles. Replaced the regulator and it worked. I noticed the slip rings were worn (like 1/8th inch groove) so that when the alternator started to act up a year later and I got a rebuilt.

I checked this one had new slip rings.

worn alternator slip rings is an issue when replacing the internal regulator.

Followup: I replaced the regulator today and it is rock solid 14.2 (13.8 with a full load). The original regulator had one of the brushes hung up so that it wasn't making contact all the time. I freed it up but put the new regulator in there since I had it apart. The slip rings looked great so no need...
One final thing, I bought a regulator from a fellow pelican (he claimed it was the same one Pelican sold but what arrived was "Hugo" brand) and it arrived without new bolts. The part where the 2 bolts go through the regulator body were about 1/2 inch thinner than the original so the original bolts were way too long. :mad:
Beware of using a Hugo regulator unless you have new shorter bolts (or want to fix it like I did).

who was it?

This was what they posted:
I have a brand new voltage regulator for sale. The part number is 911 603 913 01. I am asking $40.00 shipped in the continental US. I purchased an alternator after I bought this and don't need it. It fits 78-89 911 alternators and 78-89 928. The brand is the same as our host. Thank you for looking.
You can find the post if you care to look.