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Battery Advice - 2X6V to Single 12V (Copy w/Reply)

Started by Art, May 03, 2007, 08:01:50 PM

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Sent: Fri, 27 Apr 2007 4:49 AM
Subject: Electrical

I am restoring my 1970MGB which has been garaged for the last 23 years. I am getting conflicting reports on positive or negative ground for my two 6v batteries. The door panel says 2/70 and it is a GHN5. The motor # is 18G-WE-H32238. Some articles I read say it is Negative ground because I have an alternator, other articles say this engine # is a positive ground. HELP! I removed the batteries without checking the way I used to have them. Replacing the two 6volts has become much more expensive then it was in the early 80's!

Thanks for the help

Dan Nelson
Castaic CA 

Hi Dan,

I assume the old 6V batteries are gone and you cannot see how they were connected.  Positive ground was eliminated somewhere around the 1968 model, so I'd say it's pretty safe that the 70 you have, even if an early model, is negative ground.  Also, since positive ground was unusual for the US market, those cars are usually marked somewhere either around the battery box or under the hood.

Unless you are being a real stickler for detail, most of us with twin 6V battery cars long ago went to single 12V battery installed on the passenger side.  I am travelling and do not remember the battery size I used ( and it is not in the catalog I brought with me), but any Advance, NAPA or other battery or auto parts supplier should have the conversion number available.  It is NOT the same 12V battery as used on the later 75-80 cars and that one will not fit the box. 

You need to eliminate the series connection wire (negative to postive from battery to battery, running between the boxes) and move the ground wire to the one battery location.  You can connect the ground end to the chassis using one of the bolts on the frame of the battery box. Just make sure the connection is good (clean metal, free of paint, rust and dirt).  Or you can do as I and others did and install a disconnect switch  like the from the Victoria British (p/n 10-696) or other catalogs, though I preferred the heavier marine-type unit I got from JC Whitney.  For this, you have to replace the existing inter-battery connection and ground cable with lug-type ones to fit the switch, or just replace them with new ones suited for the job, which you can find cheaply at any auto parts store.

I hope that helps you.  Write if you have any other questions.  Good luck.

Best regards,


Art Isaacs
AMGBA Tech Staff

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