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Mark Aldridge
Frequent User
Username: mark_aldridge

Post Number: 669
Registered: 10-2008
Posted on Monday, 13 April, 2020 - 06:05:   Edit PostDelete PostView Post/Check IP

I had the passenger seat on my 1989 Mulsanne S try to readjust itself on height, rake and position whilst driving, without touching any seat controls ! fortunately I did not have a passenger and stopped the seat by switching off the ignition and then removing the seat fuses before driving off.
If this had been the drivers seat, at 70mph ,the result may have been serious. The car has a very good service history, but no record of the memory batteries being changed. I changed the batteries in both units, but the extent of corrosion from the old batteries convinced me to forget the memory and revert to electric seats without the memory unit.
This is easy in pre 1989 cars, there is a TSD explaining howto do this ( I converted my wife's Bentley 8 years ago) and all that is required is a plug in relay for each seat ( 6 each).
My 1989 Mulsanne is different and requires removal of the console to alter the switch wiring to the micro switches to copy the pre 1989 circuit which can be done but is a lot of work. An easy way round this is to fit double pole double throw momentary switches to plates in the side of the seat squab, a little agricultural but works and is quick and inexpensive.
After my experience, I consider that any fault in the seat memory is not acceptable from a safety point and if the memory unit does not respond to a new battery, then the options are as above and remove the memory ECU completely or a new memory ECU at about 450 each.
Mark
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michael vass
Frequent User
Username: mikebentleyturbo2

Post Number: 635
Registered: 07-2015
Posted on Monday, 13 April, 2020 - 18:02:   Edit PostDelete PostView Post/Check IP

Hi Mark
Who made these terrible ecu's?
With the lockdown maybe I'll get time to compare the 2 wiring diagrams and see if there's an easier way to dump the memory.
I was lucky I removed my batteries just in time.
Cheers Mike
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Mark Aldridge
Frequent User
Username: mark_aldridge

Post Number: 670
Registered: 10-2008
Posted on Monday, 13 April, 2020 - 18:42:   Edit PostDelete PostView Post/Check IP

Mike, the ECU's were probably OK in their day but age tells and I guess a 30 + year life was never considered.
Mark
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michael vass
Frequent User
Username: mikebentleyturbo2

Post Number: 636
Registered: 07-2015
Posted on Monday, 13 April, 2020 - 18:50:   Edit PostDelete PostView Post/Check IP

Hi Mark
Maybe ,but open contact relays? I thought went out with valves lol, combined with micro electronics what a mixture!
Which plugs go together Mark ,is it the switch panel and motors plugs?
If so power into green and earth brown looks like it might do something?
Don't blame be if it shorts out lol, try it through a fuse!
Mike

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