Was your headliner ever replaced? The wiring up there is that brittle thin ribbon wire that is very easily butchered when the headliner is replaced.
I do know the vanity lights work off a switch that often wears out from flipping the visor down and up. That could be the issue with your driver's vanity.
I'm assuming you've tried another festoon bulb back there. Have you checked for 12v across the prongs?
Also, IIRC, when I was hobbling together my driver's vanity to get it working, I realized the switch opens/closes the circuit on the ground side.