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Discussion Starter · #1 · (Edited)
There are many posts on this forum about the SZ seat ECU issue. I’ve spent a number of hours perusing these posts but couldn’t find an answer to my particular problem. Maybe it is out there somewhere, but I couldn’t find it. I learned a lot of good info along the way, but unfortunately nothing relevant to my specific dilemma – so I’m reluctantly initiating another discussion.

Both door mirrors and the driver’s seat stopped responding to their control switches on my 1993 Brooklands. (The passenger's seat works fine.) I just noticed this this week as the car has seen very little use this season (Covid) and as the sole driver, I did not have to adjust either since I bought the car some years back. As per many posts on this forum, this implies a dead battery in the driver’s seat ECU or other ECU failure. TSD 4701 Electrical Manual 1987-88, section 27 Memory Seats and Door Mirrors – Manual Operation, etc. describes how to bypass the driver’s seat module. The procedure and diagram within have been displayed and discussed at length here many times.

Unfortunately, the 1993 Brooklands has the later light-coloured (gray?), not brown, module. The wiring harness is substantially different than on the earlier cars covered by the ‘bypass’ procedure. It isn’t possible to simply reconnect ‘five-way’ and ‘nine-way’ connectors of the stowage bin loom on a 1993 car. There are different connectors with different number of wires on the 1993 loom.

To make things even more interesting, I opened my ECU and the battery looked fine. There was no leaking acid or visible damage to the board. The car was meticulously maintained under previous ownership (have records), so faults were addressed promptly and batteries were changed in time. When I put a voltmeter across the battery and even across the contacts on the other side of the circuit board – just to check connectivity, it gave a healthy 3.63V (rating is 3.6V). However, there could be another defect in the ECU.

I’m not concerned about the memory function, but I’d like to get the driver's seat and mirrors working. Has anyone done a bypass of the 1993-era ECU to get basic seat and mirror operation? In other words, is it even possible to bypass /delete the memory ECU and if yes, has anyone done this and could they provide some advice? Any direction would be most appreciated – even the bad news if the bypass/deletion is impossible. (Would save me a lot of time trying to figure out how to do this.) Thanks!

Attached are 5 photos showing different configurations of the driver's seat mechanism and wiring that I've encountered. In sequence: 1981 RR Silver Spirit (simplest!); 1988 Mulsanne S - someone else's car, but looks same as 89 Bentley 8; 81 RR and 89 Bentley 8 seat frame comparison; 1989 Bentley 8; 1993 Brooklands. This shows some significant changes between 1981 and the later years. Even the seat frame is completely different. That's likely because a stiffening frame member was added across the floor of the SZ cars in the later years.As such, the seat mounting points are different.
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