MGB "Electrical conversion"

I'm in the process of a complete nut and bolt rotisserie restoration / resurrection of a 1965 MGB. When I go back in with the electrical system I want to go with a single battery 12 volt negative earth system. Electrics are not my strong suit! I know some of the gauges will need to be converted, and I'm sure other electrical components will probably also need converted. I've just started doing research trying to find any checklists, or technical document outlining the requirements or best way to attack this conversion. Any help would be greatly appreciated. Thanks!

No need to covert dials. You will need to polorize the generator to negative earth upon rebuilding.

For the single battery conversion, I'm a fan of the small Miata battery:

https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=66754&SortOrder=10

There are likely cheaper places to get them. Small, plenty of power, and fits nicely in one of the battery boxes that already exist. My car has this single battery conversion, I quite like it. I use the other, now empty battery holder for tool storage using a plastic bin:



You can find the battery boxes (and the hinged cover I used) at Clark and Clark:

https://clarkandclarkinc.com/catalog/detail/battery-bins-for-chrome-bumper-mgbs

D,

Thanks! If that's all there is to do, that relieves a lot of my stress. I really appreciate the info.

Drew,

I did see a battery in the Moss Catalog but didn't follow up checking the dimensions. Great idea on the battery boxes and using one as a tool/oil holder!!!!

John B (ncbart1)

John - the Miata battery is nice in that it's small and plenty powerful for the job.

The boxes are really nice if your metal battery cages are rotted, but even if they're not they're a nice addition. I really like being able to store tools and fluids out of the way.

I can't speak to the positive/negative ground switch, but the battery change is that easy.

There's a lot of info on the internet about negative-ground conversions; see e.g. https://www.mgexp.com/article/neg-convert.html. The short story is that very little in an LBC is polarity sensitive. I'm not an MGB person, so I can't be much more specific. If you have an ammeter, reverse the connections. Some tachometers need minor changes; depends on the type. Some SU fuel pumps are polarity sensitive but can be easily modified to change the polarity. I think those are mostly later pumps, though. Reverse the coil low-voltage connections (not absolutely necessary, but you'll get better ignition if you do it.) The generator probably should be repolarized but no other changes to the charging circuit are necessary.

If you have red and black battery cables, be sure the red one is positive, so it doesn't confuse anyone who might hook up some jumper cables.

Probably there are other things that I'm forgetting.

Steve,

Thanks Man! Nice article, will be a big help when going back in with the electrical System.

John B. (ncbart1)

See the article, Polarity Change in the Other Tech Articles section of my Homepage, linked in the signature block below. The Tach will definitely need to be modified and should be done by somebody with some electronics know how. The fuel pump may or may not need to be converted to negative ground. If it is an original, points style and it doesn't have the diode/arc suppressor, no conversion is needed. If you are not sure, remove the end cover (where the points reside), snap a picture of it and send it to me at SUfuelpumps@donobi.net.
Cheers,

Dave,

Thanks for the info and offer. I'm a little ways off from installing the electrical system right now, but will add this info to my increasing file.

John B. (ncbart1)

If you are restoring the whole car, then most of this will not be relevant to you as you will build the car according to Neg earth. This is what my previous post was based on.