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MG Midget and Sprite Technical - Mitsubishi Alternator Conversion Wiring

I’ve installed a Mitsubishi alternator, and negative ground conversion, in my ’66 1098 midget after reading many postings from the archives and elsewhere. Much of what I have read leaves me a bit confused.

In an archive thread from 2001 discussing Mitsubishi alternators (http://www2.mg-cars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=archiveth&subject=97&subjectar=97&thread=2001042620555520865), it was stated, “The Alt connector resembled a "T" with the field being the top flat connection, the other connection was not hooked up. Hope this helps someone in the future.”

This is the way I hooked mine up but I wonder if anyone can shed some light on the other spade connection?

In Frank Clarici’s instructions for the installation of a Mitsu alternator he states, “The small (field) wire goes on one of the small terminals, this will be your indicator warning lamp wire.” He does not state which terminal, but from the above post I assume I am hooked up to the correct one (the horizontal spade on top).

Regarding a Mitsu alternator installation (in an MGA) on the MGAGuru website (http://mgaguru.com/mgtech/electric/ac201.htm), I’ve read “The horizontal spade terminal “R” needs a 12 volt feed from the ignition switch to power the internal regulator. This I will connect with a small (White) wire from the supply side of the ignition coil.” And, “With this separate power feed a burned out ignition warning lamp will not disable the alternator as it does with the Lucas alternator.”

Lastly, I’ve found an article about installing a Mitsubishi alternator in a Sunbeam Alpine (http://www.team.net/www/rootes/sunbeam/alpine/mk1-5/techtips/altconv.html) that includes a diagram that seems to take all of the above into account. The attached image shows the back of my alternator and the Alpine schematic.

Since my setup (following Clarici’s instructions) seems to be working properly, 14.5 volts with the engine running and the indicator light going off after the engine is started, I am not sure if I should change anything. But, if I can keep the Midget from being disabled when the indicator light burns out, that seems like a good thing.

So, if I understand the above, I should move the indicator lamp wire to the “L” terminal and add another wire with +12v, switched with the ignition, to the “R” terminal. Does anyone else see it the same way? Any red flags?

Thanks,
Paul



Paul Noeth

Paul
If your Mit. alternator is the same as what we have here it will actually charge without anything hooked up to either of these terminals but will need quite a few revs to make it charge.
R-is the sensing terminal and needs ignition switched battery power which the inbuilt regulator uses to control the voltage output of the alternator
Luckily you have power there through your globe the way you have it at the moment but it needs changing
Without this terminal connected but with the L terminal connected there would be uncontrolled output. I've had these with broken wiring and the alt.goes sky high, like 20v plus and blows every globe in site, very high speed wipers etc
The correct way to wire it is as per your last diaghram

R-battery sensing---- wire to 12v ignition source
L-warning light------ connected to ign through the warning light

Securely mount the wiring so that these little wires don't get blown about or wiggled as the engine moves and break causing the fault mentioned

If you wire it like you intend as per that last diaghram with the indicator lamp on L and another ignition switched power wire on R all will work correctly

cheers willy
William Revit

Absolutely right Willy. I have just bought a new compact alternator for a classic car (not an MG) and it had the three terminals - the large one for the battery feed, and two smaller ones, one of which connects to the warning lamp (L), and the other to an ignition switched power feed (R). This "kicks" the alt into life on first start up. On older models without this facility it isn't unknown for the alt not to start charging until the engine revs have exceeded 2000 rpm. That happens from time to time on my MGB V8.
Mike Howlett

Thank you for your input. I did change the wiring as per the diagram. The warning light works as expected and the average voltage with the engine running registers 14.6v. It all makes sense to me now.

Best regards,
Paul
Paul Noeth

I love this site
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It's fantastic
William Revit

This thread was discussed between 07/11/2014 and 13/11/2014

MG Midget and Sprite Technical index

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