Just pull the door panels off and look
It's pretty common for the power locks themselves to go bad, and it's also not unusual for wires in the door jamb to break over time where they flex as the door is opened and closed. Only the rear left passenger door and tailgate worked on mine when I got it. I checked for 12V at the harness connector for each non-working lock when the main lock/unlock button was activated, and that confirmed that it was the locks that were the problem, not the wiring. Replaced them all with junkyard units.