911 1986 Battery not charging but no warning light
 

It was a beautiful sunday and I was on the way to Caesars Head, SC when suddenly the engine stalled and the battery was dead (very painful since there was perfect Targa-weather).

However the warning lamp in the dash did not light. Later I checked if it would light at all when turning the key to position 1 and it did not. I have checked the bulb and it is working fine and is also to spec.

So I had to jumpstart the 911 (painful....a group of friendly old ladies with a '78 Chrysler helped me out) and let the cable on for 5 minutes to at least give it a little charging. It was enough to climb up the hill and park the car. Later I bought a new battery (charged one) and put it in at Caesars Head. It was enough power to let me drive back home.

When I arrived I checked the battery w/o engine running: 12.3V
With the engine running I measured 12.1V
I also confirmed that the bulb is fine again but it did not light either with key in position 1 nor with engine running.

Has somebody seen this defect and what is the clue with the warning lamp not lighting up???

Could be worn brushes, or a loose, frayed Blue #D+/61 wire preventing flow in the pre-excitation circuit for the field windings. Or, it could be a failed Voltage regulator.

Do I have to take the alternator out to check the D+/61 cable? Or is there any other way to check the control lamp prior to getting the alternator out?

It seems just strange that it does not light up at all however the bulb is fine??