The light doesn't come on at all? The light is part of the charging circuit. It light upon ignition then goes off when the alternator gives it juice..."I" would suggest removing the bulb and visually inspect and test it.

When the external voltage regulator is connected, the light glows under all key-on conditions. When it's disconnected, it doesn't come on under any conditions.

You dont want to plug up the voltage regulator because its not able to work anyway.
Marchal probably needs a set of brushes, you can do that your self.
Bruce

Brushes and bearings (it makes a terrific noise at about 2500 engine RPM) and plastic end cap. Beyond that I don't know. Parts would be necessary. I have an appointment in the morning at the mechanic's shop to see and discuss. The new junkyard alternator is back out again, too.

Solution
 

So my mechanic has another client with an automotive electrical shop in Saarbrücken, about 40 minutes from here. He got one for me overnight. I connected the wires and turned the key- lights! Ad no end play in the shaft!

So I first concluded the alternator from the salvage yard was just as dead as the alternator I took out. Then I installed the rebuilt alternator (got to use my new torque wrench!), scowled at the remaining shreds of several aluminum/paper hoses, buttoned it up and went for a drive. Problem solved.

While the car was out of commission, I managed to do a tensioner upgrade as well. Next up: Heater backdate, once ductwork arrives from Aircraft Spruce.

Thanks for all the wisdom, help, and encouragement.

Good work, send the original for a rebuild so you have one as a spare.

I found this topic after searching and reading a lot of others. It resembles my situation. I have an '81 911SC with a Marchal alternator and the external voltage regulator.

My alternator is dead. The rebuild shop confirmed it though unfortunately, they said the windings (stator) overheated and burned and that is the one part of the alternator that they cannot rebuild. They offered to sell me a rebuilt newer model alternator with the internal voltage regulator for $180. To install that it looks like I need a few parts and maybe a resistor for the bulb and would need to tape off the black VR wire. It's that easy?

$180 sounds inexpensive compared to Pelican but I don't want to buy junk and I only want to do the job once. :-) Looking at Pelican, it looks like there are two options, a 75amp Bosch for $332 and a 75amp Paris Rhone for $345. It doesn't look like there is a new option for my car, correct? It seems like I've read lots of negative comments about Paris Rhone. Why? Is the Bosch the one to get? Would I have to pay a core charge if I am not returning the exact same alternator?

Well, the rebuilt alternator for $180 is a Valeo. With no core return required, it seemed like a great deal so I went for it. It was also rebuilt by this shop not a third party so at least going forward I'll have local support and warranty. I will install it this weekend.

Anthony,

That sounds like an excellent choice.

that original external regulator you dont need i would imagine is worth a few bucks for sure ..