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MG MGB Technical - is the battery is postive to gound??????////////

does the posititve battery post go to ground??
RE HALLE

Only on a positive ground system such as the MGA used. Do not know about the earliest MGBs, but from 68 onwards they used an alternator and were negative ground. Earlier cars were generator equipped and, I believe positive ground. But, many of them have been changed over to negative ground to use more modern electronics, the majority of which were designed to work with a negative ground system.

Knowing the year of your vehicle and the reason you are asking might help us to understand what your real question is.

Les
Les Bengtson

The first MGBs were indeed dynamo-equipped and positive earth/ground, changing to alternator and negative earth with the Mk2 in late 67 at chassis number 138801.

As Les says many Mk1 have been converted to negative, if it has an alternator this is almost certainly going to be the case. But even if still dynamo-equipped it may have been converted if a PO wished to fit modern electronic equipment, but may have removed them to move the car on. period radios often had a polarity converter plug which may help. Many replacement fuel pumps are polarity sensitive, as is the electronic tach, so simply fitting a battery and giving it a go is not necessarily the best idea.

Certainly in the UK positive battery posts are bigger than negative, and have bigger terminal connectors. The bolt-up type of connector can be mangled to fit either post size, so if the connectors are better fit one way round than the other that is an indication. Only an indication mind, as I have heard of some people reverse-charging a battery to change the polarity. Fine until you come to fit a replacement and go by the post size.
Paul Hunt

This thread was discussed between 01/01/2015 and 02/01/2015

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