I was a little intrigued by the recent discussion on positive and negative
earth and conversion and
I set out to find out why there should be a difference. Eventually on a
site dedicated to Minis
(http://www.comp.glam.ac.uk/pages/staff/djcunlif/minis/miniweb/answer9.html
)
I found this.
When very early cars were built with negative earths (ie. the negative
terminal of the battery connected to the chassis) it was
found to cause excessive corrosion of the battery terminals compared to
positive earth cars. Positive earth cars also required 10%
less voltage from the ignition to produce the same spark. British car
manufacturers changed to the then superior positive earths but
European and American manufacturers retained negative earths.
Improvements to battery construction materials reduced corrosion to
manageable levels and modifications to coil construction
enabled the high tension circuit to be positively earthed even with a
negative earth system. The need to compete on the world
market forced many British car manufacturers to later revert to negative
earthed systems.
I also found a more complete treatment of conversion
http://www.universitymotorsltd.com/tech/tech008.htm
Dave Vodden
1992 Plus 4 4 seater (Negative Earth)
Hampshire UK
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