TheSamba.com :: View topic - Judson Electronic Magneto "Positive Ground"

Fri Oct 20, 2006 11:00 am

I just purchased a NOS Magneto and the box is marked "Pos. Ground" so I am assuming it needs to be installed differently than a traditional coil. I would like to install this on my 59 ghia. Does anyone know the specifics on this?

Any informationis apprecaited.

Fri Oct 20, 2006 11:54 am

Positive Earth "ground" is for British cars like Triumph, MG and others. I don't think you can use that on a negative gound car like a Beetle.

Fri Oct 20, 2006 2:08 pm

The box is marked Positive Ground but the Magneto has no marking on it. I've been told the Judson Positive Ground Magnetos were usually clearly marked on the aluminum fin like the one pictured below.

How can I tell whether this magneto is a Positive Ground Magneto or not?

Fri Oct 20, 2006 2:55 pm

yeah, it should be clearly marked somehow unless it was inked on like the one in the photo above and washed off over the years, do not attempt to hook it up if you suspect that it is for positive ground as you will burn it out, it may be possible to change the transistor or switch the wiring around but I think you would have better luck swapping it with a british car owner who has mistakenly found a negative ground one, I'm guessing the positive ground ones would be rarer than the negative ground ones? I'm sure there is a test you could perform if someone can find an internal wiring diagram for either version, the transistor current flow must be reversed and can be checked with a transistor tester maybe take it to a Radio Shack store and get it tested, worth a try

Fri Oct 20, 2006 3:05 pm

You can either PM John Moxon here on the SAMBA or you can look up the Judson Register in the UK on line and should be able to find your answer. I do know that the side terminal on the Judson is grounded to the side of a distributor using one of the distributor screws and a wire.

Sat Oct 21, 2006 12:05 am

Thanks for the recommendation Mike but I advised Reid to post a question here as I didn't have a reliable answer.

Not being anything approaching an auto electrician I didn't want to give an answer based on hearsay and that's all I have.

Reid's Magneto is NOS so it is unlikely it ever had the "Positive Ground" marking on the fin to identify it. Even more awkward is that it doesn't carry "Positive Ground" text on the label, which was the usual practice.

However Judson were a bit inconsistant on the marking of their Magnetos and all we have to go on is the "Pos Gnd" stamp on the box so we have to go along with that.

The question is, if you fit it to a negative earth car will it burn the coil out?

There is a NOS negative earth on for sale on Ebay at the moment so it might be an idea to bid on that one and resale the positive ground one. There's always a market for NOS Magnetos.