I have a 1984 Turbo 300D. Battery light did not come on with ignition.
Alternator was not charging. Did some research here on Google Groups,
and first checked the charging indicator bulb behind the instrument
panel. It was fine. The belt was fine. The battery would take a charge.
Six months ago I had replaced the brushes/regulator on the alternator,
so I had a sinking feeling that this time the alternator itself was
dead. However, I had kept the old Bosch regulator with the worn
brushes, so did a comparison diode check with the contacts on the "new"
aftermarket regulator (two slot screws take it out). Sure enough--fried
diodes after six months.  Rather than install another cheap product, I
fired up my propane torch with a tiny flame, unsoldered the good
brushes from the cheap one, and soldered them into the old Bosch
regulator. (If you do this, be careful you don't overheat the diodes.
Bingo--problem solved at no charge. Battery light now works, and
alternator charges at 14 volts.