Help With Power Locks

1989 Jeep Cherokee Laredo - most of the power option are non-functional thanks to the previous owner. :crazy:
In this thread I am seeking help with power locks.
Alright -- none of the power locks worked. Right-front window does't work, two rear windows only work from master switch. Last week I replaced the master control switch on driver's door. Now only thing improved is right-front power lock works. The replacement switch made no other difference.

Where should I look next to solve this. I would especially like to have the hatch lock working.

Not real familiar with that version of the system, but the latter systems like the 2000 had issues with the wires breaking between the chassis and the doors. You may have to splice in new wires, as needed.

And YES ! It's a PITA !

This is a situation where you need to pull the door panels and start checking wires and such. If you don't have a volt meter, a test light and jumper wires will help. One thing to start with is see if your locks are gummed up. The grease looses some of its lighter fluid over time and gets stiff. Some penetrating oil can free this stuff up and sometimes that is all it needs for the power locks to work. Also you can get broken wires at the boot between doors.

So far only checked driver's door lock, its only getting ~1.5 - 2.8 volts to the lock motor. I checked the motor itself with 12v and it works fine. The rear door's locks I haven't gotten to yet, or the hatch.

Do the lock motors work via relays, or are they directly wired?

They work directly from the switch. Check your switch to see if it is getting 12V to it. It may not. But if so, sounds like the switch contacts are not good

I guess I am misunderstanding something: If the driver-side (master switch) lock-switch is able to actuate the passenger door lock motor but not its own, how is that a result of bad contacts in the switch? Sounds more like a bad connector or three, probably buried under the dash.

I have been where you are many times. The pins on the switch where the wiring harness plug in get corroded, or the switch contacts do and you get one or more door mechanisms failing

The connectors to the switch are clean and bright. So you are suggesting the switch is bad which I just got, should I be taking the switch back? (I have never liked power locks/windows/seats.)
This may require a trip to my auto-electric genius brother who is a wiz with this stuff.

I would be checking current in and out of the switch at this point. You never know about new parts nowadays. I have gotten some bad ones