Usually that happend when the alternator is not longer putting out any juice. In your case, I suspect the brushes have worn down to nothing. No need to replace the entire alternator, but the brushes are not replaceable by them selves anymore.
It's late and my brains, what is left of them have already gone too sleep.
It is a lift off piece that gets replaced. Meanwhile, you are running off of your battery. Make sure it is charged! Turn off all electricals, cabin fan, radio, lights, etc. Otherwise you will need a tow and a new battery.

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)