XJ40 door locks

Anybody have a good understanding of the electrical door lock system in an 89 XJ40?
I (personally) installed new front door handles a couple of years ago
when the passenger door handle started feeling like it might be mechanically broken.
My electric door locks started misbehaving a few months back, going "out of sync" occasionally where some doors would lock/unlock when the key is turned and some wouldn't, etc. Recently the driver door lock stopped unlocking the door when the key was turned in the lock; I had to use the passenger door keylock to unlock the doors, and to lock the doors I had to either reach across and push the passenger side lock knob down or walk around to use the key on the passenger side. The lock panic switch on the dash stopped working at some point, but I rarely used it so I'm not sure when.
I had the car in the shop this week for other work and I asked them to look at the driver side lock, since it's a pain to have to walk around to the passenger side to unlock the door... they disassembled the door and said a worn lock lever was causing the problem, and by using some parts I had left over from my prior handle replacement, they were able to repair that lock so that the drivers door lock can now be used to unlock the car (unlocks all 4 doors). Apparently I must have used the old lever when I replaced the drivers door handle.
BUT, now when the driver door is locked with the key, the rest of the doors remain unlocked, so I still have to either stretch across the car to push the lock knob down or walk around and use the passenger door to lock the rest of the car doors. So, the shop only fixed a part of my problem. The switch on the dash still will not lock or unlock the doors. I can hear a faint click in the forward area of the passenger door when I attempt to lock the doors using the driver's side lock.
Any ideas as to what the problem is? Is there a relay or solenoid in the front passenger door that is failing (ie, a relay actuated by the driver side lock but not by the passenger side lock)? Is the control for all 4 door locks located in the front passenger door? Or what? ...ie, how are the door locks supposed to work?
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Hi Wayne,
The electrical switching for the door locks is integral with the lock motor, and in many cases is is the motor assembly that is the culprit. However, I have opened a few doors to replace the assembly only to find that it was the lock binding things. I lubed the lock and linkages and things were fixed.
Now because you can get the passenger door to operate the locking system I would say the control unit is fine. The control unit is located under the passengers knee bolster and it is a black box about 3 X 6 inches with a single white connector.
Take the drivers door apart and disconnect the linkage to the motor. Then manually move the mechanism plunger to see if the other doors respond. If they do it might be a matter of lubrication or mis-assembly to rectify it.
As for testing the control unit, I would use a digital volt meter to check the purple/brown and yellow/orange wires for momentary power as the central lock button is pressed and released. On the purple/brown wire there should be a momentary voltage drop as the door is locked. The same for the yellow/orange wire as the door is unlocked.
I hope this helps.
Blake
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Blake Dodson wrote:

Thanks for the information, Blake. Can I ask a few more questions for clarity?
When you say "motor", do you mean solenoid? Where in the door(s) is the "motor" located? What parts/surfaces do you advise lubricating? Can it be done without removing the outside door handle? (I remember it was a really frustrating experience getting that handle in proper position, with it's gasket properly aligned, when I installed it a few years ago)
Closer observation reveals that the passenger door lock seems to be the balky one, as it doesn't lock when the driver's door is locked. The console lock button does seem to work for locking, except for the passenger door, and simply clicks when activated again (ie, should it also unlock?).
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Well it does consist of a motor and a gearbox...lets call it an actuator.

It is right below the handle you installed. Its an odd shaped black box with a short rod connected to it.

Lube anything that slides, pivots, or moves. A light lithium grease will do. Also make sure nothing binds or has resistance.
Blake
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