Well, I'm going to guess that you are working on the 95 truck you have listed in your signature, since you used the word "truck". It's a little tough since I don't have a schematic on that. I assume these are manual locks where you are hitting a switch to open or lock them. One of the leads into the driver's side switch has to have 12 volts to ground all the time. Might start there. Doesn't sound like a lock actuator problem because both the drivers and passengers either work or don't work.