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MG MGB Technical - overdrive switch

Any help please

I am installing a LH type overdrive trans in my 70 mgb and there is no wiring in place . Can you simply wire a 12volt on off switch to the solinoid to engage and disengage overdrive .

Thanks in advance Derek
Derek

Proper wiring for the overdirve will go through a switch on the transmission to prevent the overdrive from being active while the transmission is in reverse. If the overdrive is engaged while the transmission is in reverse, it will ruin the overdrive. This switch also limits the overdrive to 3 and 4th gear. This part depends on the overdrive, some of them are wired to work only in 4th.

All cars were wired for overdrive in the main harness. look at wiring diagram for your car. I believe the wire is yellow and for a 70 car it will terminate close to the turn signal switch on one end and the other end will terminate near the wiring for the reverse lights on the transmission.

Check the archives. There is lots more information on the wiring, including adding a fuse, there.

Cris
Cris DeYoung

Have a look at Advance Auto-wire on the web.It got wire diagrams if you hvaen't and is helpful with eugrading wiring
Bob
R Etches

The URL for Advance Auto Wire is: http://www.advanceautowire.com/
David DuBois

All MGB's of this era are already wired for the OD.

Look for an unused bullet connector (Yellow wire) somewhere
in that bunch of bullet connectors that is near the forward edge
of the shelf that the Charcoal Canister is mounted on.

That Yellow wire is already connected to the OD switch on
the Wiper Switch stalk - and it's powered, too - and so there's
no need to fumble under the dash or take apart the steering
column cowls, etc.

Of course, you could always test this lead with a voltmeter.
Daniel Wong

"This switch also limits the overdrive to 3 and 4th gear. This part depends on the overdrive, some of them are wired to work only in 4th. "

Not correct, whether the OD operates in 3rd and 4th (up to 76) or 4th only (77 on) depends entirely on the shape of the selector rod where it operates the lockout switch, the OD itself is the same in both cases. It was changed to 4th only because a switch was needed to operate in 4th gear only for the TCSA and it was cheaper to remove OD from 3rd and use the existing switch than engineer in another switch.

As Daniel says the manual OD switch was always on cars with the column wiper switch - just pull the switch towards you for OD and away for non-OD. The ignition has to be on and the switch pulled towards you before you see 12v on the yellow wire coming out of the main harness by the fusebox. This is unfused, it makes good sense to fit an in-line fuse between the main and gearbox harnesses, use a standard-rated fuse. While you are at it fit another where the white from the main harness joins the white to the rear harness for the fuel pump.
Paul Hunt 2

This thread was discussed between 28/05/2006 and 29/05/2006

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