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Pos/Neg Earth?

Posted: Sun Nov 09, 2014 9:41 am
by Heronwood
HI All,

I posted this in this forum as I think I might get more of a response.

I have a dilemma!

I recently purchased a series II 1954 Minor. it had been in storage for 40 years, the seller put a battery on and some fuel and she started up fine and runs perfectly. However she does not charge and the battery goes flat.

On close inspection the previous owner had just put a battery on for starting purposes, it was not the proper battery and was ill fitting, the restraint strap did not fit, so the fitting was done in haste for me to see the engine ran ok.

He put the battery on as if the car was pos earth.

On close inspection the earth strap has a negative sign on it.

This has got me thinking that the car may have been converted to negative earth at some point.

i. If the car had been converted to neg earth and the battery was put on in the pos earth configuration could this account for the
lack of the charging issue?

ii. If (as in i above) the battery was put on in the pos configuration would the car start at all?

iii. The previous owner has recently fitted a new fuel pump,( my other car is a 67 MG roadster and when i restored it I had to
purchase a negative earth fuel pump) could this be a clue as to the polarity?

iv. How can i test if the car is neg/pos earth for sure?

v. Why would someone put a negative marked earth strap on the car as the battery is difficult to connect if the car was still pos earth, the bat terminal is a different size?

Thank you in advance for any comments.

Mike

Re: Pos/Neg Earth?

Posted: Sun Nov 09, 2014 12:16 pm
by mike.perry
If the car has been untouched for 40 years then it is unlikely to have had the polarity changed as many cars of that era were still using pos earth.
The polarity would not affect the fuel pump as this has a a throwover action which works in either direction
Check that the dynamo is working and the brushes are not stuck, disconnect the fan belt and connections and attach jump leads to the case and field terminal and it should spin.
Don't worry whether it is pos or neg, just polarise the dynamo to whichever you want

Re: Pos/Neg Earth?

Posted: Sun Nov 09, 2014 4:17 pm
by Heronwood
Hi Mike,

Thank for the advice. Why do you think the earth strap to the battery would have been changed? it has 'neg' stamped on it..
Mike

Re: Pos/Neg Earth?

Posted: Sun Nov 09, 2014 10:34 pm
by bmcecosse
" Case and field terminal " errrr not quite!!

Re: Pos/Neg Earth?

Posted: Sun Nov 09, 2014 11:01 pm
by mike.perry
Maybe the original earth strap was knackered and that one happened to be lying around. On a car that is 60 years old anything could have happened, you cannot take anything for granted