The Yellow and Blue wires from the pass. side door lock actuator come through the rubber bellows at the hinge and go up into the dash. Sounds like you've already figured that out. Above the passenger's knees (behind the black felt panel) there should be a Blue plastic connector which joins the door wires to the Yellow and Blue coming from the lock/unlock relays. You will get a clear view of all this if you remove the glovebox.

If the wires and connector from the relays (which are located just below the central air vents) are not visible, someone has either cut them out or pushed them aside somewhere in there. If you find and reconnect everything, you may discover why they were disconnected ie: like Sven says, there may have been a problem with shorting out. If so, it's pretty easy to pull the inner door panel and trace the wires from the actuator to find the bad spot.
--
Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD and 89 745 (LT-1 V8); hobbycar 77 MGB, and a few old motorcycles)

I'm sure the Bentleys book has it.
Haynes has a diagram for it.
Rube Goldberg would be proud of the design. It's pretty complex.
I'm sure someone else will respond that no, it's really very simple - but there are at least two relays, one or two switches, five motors (counting the cargo lock) and a whole lot of wires, mostly hard to get at.

Often one of the switch(es) in driver's door will go bad or a wire will become bare and ground out within the door. Then someone fixes it by disconnecting the system somewhere. I wouldn't be surprised if that's what happened on your car before you got it.
--
DAMHIK: Don't Ask Me How I Know - - - Sven: '89 245, IPD sways, electric rad. fan conversion, e-codes, 28+ mpg - auto tranny. 500 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).