Remove the voltage regulator (2 Philips head screws on the back side of the alternator) and inspect the brushes. If both brushes aren't shiny then there probably isn't good contact with the armature. The springs are only so long and can't apply enough pressure when the brush material thins beyond a certain point. You can replace the brushes if you're a true DIYer or replace the voltage regulator.

Could be you drained the battery beyond the safe depth of discharge but I'd think a working alternator would have kept you going.

Sixto
93 300SD