I have posted in the other old thread
Drivers Power Seat
but have no response, so I am rephrasing my question.

My mechanic believed that the seat ECU on my driver memory seat (RHD) was faulty because all relays and motors were checked to be in working order but the seat was not working in any direction. I looked up the JaguarClassicParts website, TSBs and various forums and learned that the 15A fuse should be replaced by 20A and the original ECU LNA2165AA has been superseded by LNA2165AD. So I asked my mechanic to replace the fuse while I bought a used ECU LNA2165AD from eBay. After fitting the ECU, the driver seat remained motionless and the mechanic found that the seat received no power. These leave me to wonder
(a) whether the replacement ECU I bought from eBay was no good (it carries a Jaguar's Label clearly stating Part No. LNA2165AD with memory function for X300, but the eBayer said it was removed from an S-type (LHD) and would also fit similar models from 2000 through 2002);
(b) whether there are other seat relays situated in weird locations which I may have missed; and
(c) whether there are other wiring issues.

Meanwhile I notice that all eBay listings for the used ECU 2165AD claimed that the ECU was removed from US cars. Strangely, there is no memory seat ECU from other RHD regions. The labels on the ECU sometimes says "Issue E" or Issue "F". Wonder if the memory driver seat ECUs are different for the driver seats of LHD and RHD cars, or there are other reasons blocking power supply to the driver seat.

 

I eventually bought another Memory Seat ECU off eBay from Australia, but like the previous one it fails to reactivate my driver's seat. My mechanic is bewildered as all relays, fuses and seat motors are found to be in order, but it is unlikely that all three ECUs, (the original, the one from the US and now the latest one from Australia) are faulty. There simply isn't any power supplied to all of the seat motors, and it is also unlikely that all control buttons on the seat have failed at the same time. Have I overlooked anything that might interrupt power supply to the driver's seat?

 

Have you checked the earths? On the 12 position connector that plugs into the seat module, pins 3,5, and 9 should be black wires and go to earth. The pin numbers on the connector are very small, but they are there.

On the 22 position connector (also blue) pin 15 should be an ignition switched ground. With the key in position 1, you should have continuity to earth. That wire is white with a brown tracer. Pin 11 (white/purple) gets power from the RH heelboard fusebox ( under the rear seat trim panel, carpet covered), fuse #12, 10A, only with the ignition in position 2 (i.e. run)

On the 12 way connector power should be at pin 7 (brown/orange), pin 4 ( brown/green), pin6 (brown/light green), pin 12 (brown/slate)

Pin 7 gets power from the LH heelboard fusebox, fuse#6, 5A.
Pin 4 gets power from the LH heelboard fusebox, fuse#3, 20A.
Pin 6 gets power from the LH heelboard fusebox, fuse#4, 20A.
Pin 12 gets power from the RH heelboard fusebox, fuse#9, 25A.

 

Many thanks. Will double check; mechanic said he added ground before and didn't work; live link also failed. I read many posts in other forums and one possibility is the seat harness. Am using the primitive method of powering individual seat motors to reach best driving position as a temporary solution.

 

At least you know the seat motors work!

 

Here is an update. Eventually, the remaining suspect is the seat harness. Bought one form the breaker and bingo! The old one seems compromised due to corrosion and physical damage (see pictures).



The driver power seat now works in all directions except up and down. I hear the motor trying to grip though, so maybe it is time to find a replacement motor.

 

That is one hideous looking wiring harness! How was that not discovered back in 2017, was it all concealed damage? What about the other two seat ECUs, do they still work?

As you might be aware, the seat motor drive cable can come loose from the motor, so you would still hear the motor, but it will not move the seat. Pop the square ended cable back into the motor. A common failure for the up-down movement, but a free and easy fix.

 

Yeh, I think the mechanic at the time was more concerned with investigating the no-start syndrome, and it was too much work to remove the seat for a more thorough inspection, and there was a temporary fix to adjust the seat by by live-wiring the various motors. Anyway, will now concentrate on tackling the up-down movement failure.

And, yes, the two seat ECUs that I bought are in good order, so is the original.