The Batt light comes on solid when igniton turned on, so that is normal.
I'm thinking alternator failure, although I'm hoping it's the belt, but there is certainly no slack in it.
I have 2 spares, but all 3 are new- this one was installed when the engine went back in, last year, this time. At least 12kmiles

When time allows, I'll take it off, and check out all of the pulleys, etc.
The


85 WR quattro
90 V8 Silver, 91 V8 Black, 93 V8 Lago
93 100e quattro V6. Titan, i think