I am trying to determine why the central locking system is totally dead.
I found that there is no battery power going to the Brown/Green wire at the Door Lock module DBC1554.
This wire is connected to a brown wire coming from the Engine Module DBC10234
On the two harnesses connected to the Engine Module there are no other wires that carry battery voltage with the key in the 'off' position.
There is also no voltage on the brown wire with the key 'on'
Based on the electrical schematic I have (1991MY) there should be constant voltage on the Brown/Green wire going to the door lock module
I disconnected the Brown/Green wire from the connector with the brown wire coming from the Engine module and applied 12v to the Brown/Green wire and three of the four doors lock and unlock with the key. I will have to see what is wrong with the left rear door.

Since the Brown wire with the connector shown in the photo does not have battery voltage and it is coming from the Engine Module which is riveted together so I can't get to see inside, what is my next step?
Also, the door lock switch in the center console was not working. I opened the switch and cleaned off some corrosion.
I reinstalled the switch and now I can hear a click on the passenger (right) side door only.

 

Anyone with knowledge on this topic?
In the interim, I am going to leave the Brown wire coming from the engine module disconnected and run a separate wire to the door lock module with constant power so I can figure out why the left rear door, boot lid and fuel filler flap don't work.
Is this the correct thing to do? or should I wait for someone to give me some advice.
As per the electrical schematic, the Brown/Green wire at Door Lock Module (DBC1554) is supposed to get a constant 12v from Circuit #50 which I will presume is the same Brown wire coming off the Engine Module(DBC10234)
When I apply 12v to the Brown/Green wire and ground the small red wire at the DLM three doors lock; when I ground the small purple wire at the DLM three doors unlock.
Left rear door, boot lid and filler flap not working.

 

I have temporarily tapped battery voltage to the Door Lock Module.
As stated above, only 3 doors work.
I am looking for a door lock actuator for the left rear door.
I removed the actuator and opened it up. The little motor is stuck solid.
I tried to free it up but it seems as if something is broken inside.
If anyone has a known good actuator, please PM me with a price + shipping to zip code 32935.
In the meantime I will be visiting the JY tomorrow. There are 2 XJ40s there. 89 and 90.
I am going there to pick a driver front door and fender. I will see if the actuators are there
See damage to my car in my post "HIT AND RUN"

 

sanchez I'm working on the exact same problem, I guess its wise to share what each other come up with. So far I've replaced both of my rear door 2-wire actuators because they did not work when I applied direct voltage to them, the new after market ones work fine when I push down the driver door and passenger door lock. But still nothing happens when I turn the key to "unlock", and only one of the front doors and both rear doors locks work when I turn the key to "lock" the doors. So I'm going to do what you've done by checking the voltages on everything and let you know what I come up with. Hang in there, we will eventually figure this out. Cheers.

 

Thanks. I need all the help I can get. Try this.
Remove the 2 screws that hold the door lock module in place. With the connector in place,take a test light, ground the clip and touch the small red wire. that will ground the red wire lock circuit. Next to the red wire is a purple wire. Touch the test light to the purple wire and that will ground the unlock circuit. The other small wires are for the filler flap and trunk.
At the faulty actuator connect a DVOM to one of the two wires and touch the other. Have someone activate the door lock with the key. You should either +12v or -12v. If you reverse the connections, the one that had +12v should read -12v and the one that read -12v should now read +12v. The voltage will be momentary.
That is how I determined that the door lock actuator was bad since one wire went to ground when the other was seeing 12v and vice versa. So the circuit is good.
If I am not mistaken, the driver and passenger front door lock actuators have 4 wires. 2 inputs and 2 outputs which go to the rear doors. I am not sure. Will check if that is correct sometime over the weekend. Trial and Error is all I have.

 

Well whatever it is in my situation it has to be either the Driv lock switich or the Pass lock switch (which are an integral part of the actuators, here's what I have already.
1. Neither side works with the key to "unlock" the doors.
2. Each front door lock will "lock" and "unlock" the rear doors only by pressing and pulling up on the door lock knob. Each front door lock will not lock or unlock the other front door.
3. Since the 2 front door locks are on the same circuit, that will be my focus. I highly suspect a short in one or both of the front door actuators since there is no signal between the two of them. What do you think? There is obvious power to each of the front locks because they will operate the 2 rear door locks..

 

By the way Sanchez, I've disconnected the trunk locks and my model doesn't have filler cap lock, its cable operated. The front dr actuators have 5 wires each.

 

Finally, I have all 4 doors locking and unlocking with the key in either the driver or passenger door. The switch in the center console still does not activate the door locking function.
I still have to work on the trunk(boot) and fuel filler flap.
To fix the left rear door problem, I followed some pictures about opening up the actuator motor as was posted on the Jag lovers forum.
Opening up the motor, I saw that one of the brushes was broken. To fix it, I opened up the electric motor from a battery operated toy car that was laying around for about 15 years.
The brush was a little bigger that the one I needed so I filed it to the proper size and installed it in the actuator motor.
I tested the motor with a 9v battery and it worked great.
I put the door lock actuator back together and tested it again and it gave the motion of lock and unlock.
Installed actuator in car and it works. For how long is the question.
I was so excited, I forgot to take pictures. Now on to diagnosing the trunk and fuel filler flap.
Heading to the JY tomorrow to pick up a front door and fender for the project in my post "HIT and RUN"
At this JY, you have to pay and they pull the parts for you. I will now have an extra front door actuator but Vandenplas90 states that the front door actuator has 5 wires.
Can it be wired up to serve as a rear door actuator?

 

Congrats of repairing the actuator motor. I simply replaced my rear actuators with a couple of cheap aftermarket ones and they work fine. What I'm starting to realize is that my two front actuators are most likely shot as well and I'm waiting for 2 aftermarket 5-wire actuators to replace them as well. It seems very logical that all of my actuators are shot, the car sat unused for many years, only 12k miles were on it when I bought it in 2008, so that's where my focus will be. Good job and good luck.