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MG MGA - Changeing polarity and fuel pumps.

Hi all,
I am intending to change from postive earth to negative on my 1960 MGA. I have read up on it and it doesnt seem to bad other than around the fuel pump. Some pumps will work either way and some are polarity sensitive. Here is my pump, how can I tell whether it will work OK once changed. I dont wont to damage it.
Any help on either changing polarity or fuel pumps will be very welcome.

s page

If you look inside the bakelite cap you may find an electrical component wired across the contact points the purpose of which is to get rid of the electrical energy stored in the coil when the points open. Otherwise a spark is generated across the points which will eventually burn them away.

The type of component used to suppress the spark has changed over the years from a capacitor to a plain diode to a voltage dependant resistor to a back to back avalanche diode. If you have a plain diode wired across the points your pump will be polarity sensitive.

If you can't tell what the component is by looking at it and you do not have test equipment then you could buy the latest device from here:-

Your pump will then be polarity insensitive and it will only costs you a few pounds.....................Mike

Mike Moore

S. Page - The arc suppression device in the pump that you have is difficult to reverse due to the fact it is manufactured to go in place only one way. Mike's suggestion of a Transil is an easier way to go about changing the arc suppression device. The picture in the Totally T Type shows the the Transil being installed across the points, whereas I prefer to install it across the coil. that said, it should work equally well either way. If the offer from John James is no longer available, contact me at and I can send you one for the cost of postage. Cheers - Dave
DW DuBois

Hi All,
Many thanks for your help. I have just taken the pump of to see what I am dealing with. It looks to be a newish S.U pump and on a label is stamped AZX1331 which equates to a dual polarity pump. So all good and one step nearer. I have found in stock a later negative tacho so my next job is to sort out the wiring for it. 1800 engine is going in as well.
regards. Simon
s page

This thread was discussed between 26/02/2017 and 27/02/2017

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