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MG Midget and Sprite Technical - MG Midget 1963 - New battery now Tach U/S

Hi
WE have a 1963 midget, the battery failed so I purchased and fitted a new one. I assumed the Midget was still pos earth so connected it that way, now the rev counter and radio do not work. If the car had been converted to neg earth at some would these be the symptoms? Everything else seems fine.

Regards

Keith
Keith Weblin

I don't think your generator would work either. Is it recharging? It's easy to repolarize the generator, less easy to rewire the tach, easier to determine how it was before the battery swap and make sure it's that way now.
I rewired my '63 recently and converted to negative earth at the same time, including rewiring the tach (which is pretty easy really). I'd suggest going through it as if you were converting to negative earth and check everything. Here's a tach picture I took. Swap those wires and reverse the loop.


J Van Dyke

Keith,

Take a look at the Tach Dial - it will have written on it near the centre whether it's for positive or negative earth.
Adrian Jones

Keith

Oops! Looks as if you've got the battery the wrong way round. It does have different sizes posts for POS ans NEG unless someone has fitted the car with a battery with lugs.

The Radio has probably had all the transistors blow up and will be difficult to find replacement transistors if the radio is old, although it is slightly possible that you may have a valve (tube) unit as these were still around in the sixties.
An old radio of that time should have a polarity plug to move to get the correct polarity. Take the radio out and look. If you have a valve radio it may still work when correctly connected. There were hybrid radios availble at that time which ran on 12 volts with a single 'large' transistor to drive the speaker. This transistor will certainly have been blown with reversed polariy. Good news is that you can probably find a suitable transistor at Maplins. It will be a PNP type Germaniun transistor.
The Generator does not need to have any wiring changes to reverse the polarity. Take both the leads off and "splash" the field terminal ( the smaller one) with a wire connected to the live battery terminal. This will set the residual magnetism in the correct sense for the generator to work, but also check that the cut-out in the hasnt welded its contacts. Your battery will discharge rapidly if it has. Good hunting Arthur.
AG Martin

This thread was discussed between 12/07/2009 and 13/07/2009

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