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Overdrive inhibitor switch

Hello all, for a while I have been trying to sort a non-functioning overdrive on our LE Roadster.

I am aware that the inhibitor switch (prevents use in 1st, 2nd and reverse) is on the N/S of the gearbox, and fairly well forward out of easy reach.

What I would like to ask members is: is it in anyway possible to change this in situ - without removing engine and gearbox, or cutting a hole in the gearbox/transmission tunnel?

I am fairly good with working where I cannot see whats going on, so sensible suggestions welome.

thank you


Hi Valerie

The inhibator switch is very difficult to access / remove whilst in the car .

1-Have you checked that it isn't a wiring fault (the harness which connects on the bulkhead near the heater is a common issue) ?

2-Also have you tried bypassing the switch itself and then raise the rear of the car in the air and run the engine/ engage 3rd and 4th gear (DO NOT ENGAGE REVERSE) to see if the overdrive works?

If it ain't broken don't try to fix it as if you do it will definitely break

Hello Colin,

I have checked the wiring on a tester and get current at the solenoid bullet,  but when I connect the solenoid it and engage the OD switch (in 3rd or 4th) it doesn't activate.  When i bench test the solenoid direct on the battery it kicks in.

The wiring at the join near the heater bulkhead seems OK, I have managed to change one terminal on the OD inhibitor, but this doesn't seem to have helped.

I did wonder if it was possible to bypass the inhibitor (Only to test the OD) to make sure its working, i have pretty much done everything else, oil, filters, pump, magnetic plates, gear lever switch, so it cannot be much more.

Thanks for the advice




Hello Valerie,

It is possible to change this switch in situ but not easy and not cheap. A local MG restorer I know can do it and charges I believe £150 - £200  plus the cost of the part, so it must take a few hours to gain access.

You could call him and he may be able to advise.

He is Alan of AC Restorations on 07717 071698.


Hello all,

On the same subject of the OD again, it appears that our wiring is not standard to the wiring diagram for the OD, it does not run directly from the fuse box to the OD switch in the gear lever.  Instead it runs forward to a silver Bosch relay unit (which I cannot figure out why, or what it does) i am posting some pictures here in case anyone has seen this arrangement before and can offer some advice?  First thing i thought was a re-wire from the 3rd fuse box spur, via a fuse to the gear lever.  I have just about exhausted all options and am pretty much stuck now.

Many thanks

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Thanks to those that replied, it turns out that the middle relay was added as part of an aftermarket alarm/ignition isolation type system.

Removed all the extra clutter, and wired the OD directly from the now spare fuse box terminal (via in line fuse) and the solenoid worked fine.  In test drive OD now works as it should. Somehow the extra relay and wiring was controlling the OD?

Thanks to those that replied with advice.