MGB & GT Forum

Newer MGB (>1977) have the interlock switch wired first: See schematic. Are the interlock wires (buletts) going to the engine bay? and are there connected to the OD switch?
Konrad

I'm not sure which market your car was manufactured for, but the uk market doesn't appear to use the inertia switch, so it od switch to interlock. Dick Moritz should be along shortly.

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Ben
1966 MGB Tourer
1973 MGB Tourer

It is not about the inertia switch, but the gear-interlock-switch closed in 3th 4th gaer to prevent overdrive in 1 and 2nd.
I think it is true for all MGB after 1976 (77-80).

+1 on that Konrad. Are you certain yours is wired that way, that you have the correct wiring diagram ?

Most of the non US market circuit diagrams I can see right up to 1979/80 start with the OD on/off switch then a yellow wire going to the gearbox's interlock switch and Red/Yellow (sometimes Yellow/Purple) out to the OD solenoid

What is it you are trying to accomplish?

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

To be honest, my MBG-GT is of 1975 and not wired as in the schematic. My gear switch is after the OD Switch just before the solenoid.
My Overdrive Controllers (ODC) are connected between the OD Switch and the gear switch. This way it is powered through the OD Switch even when the interlock switch is open.
This is essential for the correct function of the ODC. MGB from 1977 seem to have the wiring as in the schematic shown. In order to modify the wiring to be used with my ODC it
would be simpler if the interlock switch is going through the engine bay! I could then give advice how to modify and hook up ...
Konrad

The schemtic is part of the AutoWire Schematics 77on .....
Maybe only the US car have been wired like this, but it looks as MGBs have been manufactured this way ....
Konrad

In your 1975 MGB the overdrive on/off switch is built into the wiper/washer stalk on the right side of the steering column. Presumably this is true for RHD cars as it is for LHD cars here in the states. There is power supplied to this stalk switch for the overdrive function, and there is a wire going from this stalk switch, through the firewall, ending in a yellow wire with a female bullet connector just aft of the fuse box in the engine compartment. This is true for all MGBs 1968-76 regardless whether or not they were factory equipped with overdrive.

From 1977-80 the overdrive on/off switch was moved to the top of the gearshift knob; hence the different wiring arrangement...

From the factory, and with the small additional overdrive wiring harness, this yellow wire is connected to either terminal of the overdrive lockout switch located on the remote control housing of the gearbox. Then a short wire connects the other terminal of the lockout switch to the solenoid wire. If this helps:

12V > stalk switch > lockout switch > solenoid

This arrangement allows overdrive only in fourth gear on later cars, and only in third or fourth on earlier cars. It prevents engagement of the overdrive in reverse (as well as in lower forward gears...) in order to prevent damage to the unidirectional clutch within the overdrive unit.

There were no overdrive controllers installed from the factory. If you have some sort of add-on controllers, you might explain their function and design for further help here...

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Dear Dick,
Thank you for your explanations. I really do know the wiring of my car . I changed the OD switch back to the dash, as earlier cars, because I hate to actuate the wipers by mistake.
I do have a ODC2321 built in, now actuated by a momentary toggle switch and I did add a LED to show the real Status of the OD. If you want to know details of my ODCs, go to my
homepage Swiss-MGB and go to "Projekte".
Some downloads are translated to english and detailled function is explained.
My question was to help owners of late US-MGBs hooking up my ODCs .....
If you still have questions, just ask.
Konrad

Can you provide 2321 in English?

Thx,

Dick

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Never mind. Figured it out. English translation below for folks who may be interested...

Apparently what this does is switch on the overdrive when desired, but automatically turns off overdrive when shifting out of third or fourth, so if you leave the switch on inadvertently, the gearbox will default to direct (non-overdrive) until the switch is switched to On again...

Dick

This document is identical to previous ones except for the circuit and its description
Publications on Overdrive Controllers (ODC). The improvement concerns the simpler one
Function operated by an illuminated pushbutton, which activates the toggle switch
Dashboard replaced. The push button fits into the hole of the toggle switch.
This ODC can be used for Laycock overdrives type LH (in MGBs from 1968).
become.
introduction
By default, the overdrive is operated with a (toggle) switch. Do you forget that?
OD to turn off when you use the 3rd/4th. Leaving gear will be in when shifting up again
the 3rd/4th The overdrive automatically switches back on, which is usually the case
is undesirable. To prevent this, I built a small piece of electronics
is extremely easy to install without changing the existing cabling. For this reason
The original condition can be restored within seconds.
The two flat connectors (yellow and white strands) are removed from the toggle switch and turned on
connected to the pre-assembled illuminated pushbutton. For the lighting function
(optional) an additional strand (vio/gb) must be laid

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Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

I do attach the PDF for anyone interessed in the ODC2321 and a picture showing the alternative to the illuminated pushbutton.
All PDFs can be downloaded from Swiss-MGB. I do answer any questions related to it.
Konrad