I'm having trouble getting this thing running...

The fuse is good and the relay works. Light switches on and I confirmed that I am
getting 12V to that first wire, screwed into the pillar (driver's side) behind the trim above the back seat. I pulled the trim on the passenger side and found a similar wire though the screw I guess had vibrated itself out over the years. I'm guessing this is a ground? I installed a new screw and reconnected that wire to the pillar.

Still nothing happening when I flip the switch.

I have no idea what I'm doing back there and couldn't find any diagrams online.
What's the next step after confirming 12 volts are making it to the driver's side rear?

__________________
1981 240D 4sp manual. Ivory White.