need power door lock help

1985 chevy 1/2 ton. Power windows and locks. driver side switch actuates the passenger door but not the driver door. Installed new actuator and still the same. Switch is obviously ok. All wiring in the door looks good, no corrosion. I know I need to start tracing the wiring into the cab, but can anyone suggest a starting point where the left and right door wiring interface? is there a relay or something. I've never worked on this year truck before and would rather not just start pulling panels off .

thanks, Chris