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MG MGB Technical - Overdrive Dash Switch

Hi,

Just a small question about my '78 MGB GT. There is a switch on the far right of the dash but I have no idea what it does.

I looked in the Haynes manual and there is mention of an overdrive switch on the dashboard but mine doesn't seem to do anything, plus I have a o/d switch that works just fine on the gearstick.

Can anyone tell me if this is supposed to be another o/d switch and hazzard a guess as to why it doesn't work?

Thanks,

James
J Elliott

78s had their OD switch on the gear knob - the switch on the dash sounds like a PO mod - look behind the dash and see what wires (if any) are attached and find out where they go.
Chris Betson

As Chris said, OD should be on the gear stick. However, the 76 onwards cars had a large expanse of plastic across the drivers side of the dash, with the metal shell underneath. There was also a change to a single gauge for the oil pressure with water temp moved to the right side of the s/wheel, and fuel tank mounted centrally between the rev and speedo gauges. Also the rev and speedo went to 3 & 1/2" dials.
The reason for this is you may have an earlier dash where the switch may have been fitted in the previous OD switch location (pre74).
Several possibilities spring to mind if the PO did fit it.
A switch for a spot light relay.
A theft deterent switch for the fuel pump or starter.
Martin

I have often heard of a "correctly placed" overdrive switch put on the dash, despite there being one on the gearstick.

The gearstick switch operates the overdrive and as martin suggests, the dash mpounted switch operates a fuel pump or battery cutoff switch as a theft deterent. To the uninitated because the dash switch has "overdrive" stamped on in big letters hopefully they will leave well alone when trying to illegally make off with your car.

First check behind dash that it is connected and try to follow wires. If no luck, then try switching it to "on" and run car for few minutes. If it is a fuel pump kill switch, the car should run out of fuel after the fuel in the carb fuel bowls is used up in a few minutes time.

I would hve thought the PO would hve explained if he had fitted such a device however, but you never can tell with some people....

Regards ~PHIL
Phil

My 80 B has a gearstick OD switch but I’ve used a dash overdrive switch (looks authentic and also works well) as an override switch for the electric cooling fan.

Brian
Brian Davis

Thanks guys,

The switch is a temporary up and down switch. I'll send a picture to a couple of you in case it is just me being stupid and it's something simple.

I have tried it on a few occasions but didn't see anything happen so didn't think anything of it.

There was only one previous owner and she had it since new.

When I go home this weekend I'll try it and see what it does (I'm at Uni in my final year at the mo and the MOT has run out and I'm going to restore it this summer else it won't pass the next one).

Cheers,

James
J Elliott

James
My 80 GT doesn't have a mounting hole at all on the bit of metal dash showing to the right of the plastic dash (next the temp gauge), so if your dash is original, I would have thought the hole would have been deliberately drilled (unless there was a dash change post 78?).
Unless the wires have been tapped into the loom near the steering wheel, then the wires should be realtively easy to follow through to the engine bay if it is a theft deterrent or cooling fan override switch.
Keep us posted on what you hear from the PO.
Martin.
Martin

Curious. My '77 roadster came with a hole in the early O/D switch location, cunningly plugged with a blanking grommet. Since the finish of the dash goes over the edges of the hole, I'd assumed that this was an original "feature". I've since bored a hole in the grommet to stuff a flashing LED into as part of the "immobiliser" (alright, switch in ignition circuit).
Tim Cuthill

James sent me a photo - the switch is not the standard OD switch but a three way passing toggle switch with a central resting position. The escutcheon behind it has up and down pointing triangles so I wonder whether it was a switch for an electric aerial......only tracing the wires ( if any) will solve the riddle.
Chris Betson

Chris,

I think you just hit the nail right on the head.

The car did come with an electric ariel but it wasn't working (completely rusted) and I had to take it off. I thought it would have been connected up to the old stereo but come to think of it, when I replaced it there was only a live and an earth cable so that switch on the dash must have been connected to the ariel!!

I just taped the old electric ariel wires up under the bonnet for when I had some spare cash to buy a new one.

I forgot about that!

James
J Elliott

This thread was discussed between 14/01/2003 and 15/01/2003

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