200 TQ alternator squeal, then no output

[Kurt Wesseling]

Greetings alternator fans,

Patient is my '89 200TQ, 183k miles.

What I thought was the alternator belt has been squealing with increasing
regularity of late.  When this happens the volt meter drops to 12 volts the
lights dim,etc. Usually if I reduce current load by switching off the seat
heater, turning off the headlights briefly, etc the squealing stops and
voltage returns to normal range...until last night.  Naturally it was a 10
degree F with a 30mph wind night.  Sequence was, squeeeeeeel, low voltage,
lower voltage, still lower voltage...turn off all electrics--except low
beams--no street lights in the boondocks of Maine.  Finally the battery can
no longer support the fuel pump, so she dies. Flatbedded her home.

Today I go out and she starts right up, volt meter showing normal range
again! Go for a test drive, 2 miles later squeeeeeal, NO output again.  Limp
home, lift hood, alt is not squealing, belt is turning--not slipping, and
all looks normal--except there is still no output--at least no more than 12
vdc indicated presumably from the battery.

So what's shot? Bearings, brushes? Avi, Huw...anybody??  8-]

Thanks,

--Kurt