The theory is well proven in other areas, telecoms cables used to be lead
covered and in the days of electric trams with earth return through the rails
and ground the currents could literally cause the lead to transfer from the
cable sheath into the ground. The telcos counteracted this by burying lead
anodes in the ground connected to a voltage supply which balanced the current
flow in the cables and the 'sacrificial anode' was destroyed instead.
I did remember hearing at the time of the change of car polarity that (one of)
the reason(s) was electrolytic corrosion, but if you reverse the polarity
something else has to corrode, so what that was going to be I can't recall.
It would only happen where there were electrical connections, so maybe it was
supposed to be the terminals bolted to the body that corroded instead of the
body, but I can't say I have ever seen any evidence of that. In any case the
other side of the electrical circuit i.e. where the battery connected to the
body instead of where the components connected to the body would have reversed
potential as well and so in theory that would then corrode at the body
instead.
But that could only affect ground connections to the body as I say, not
corrosion elsewhere. That is either caused by exposure to the elements, or in
the case of most volume manufacturers in the late 60s and 70s when costs were
rising rapidly they were buying cheaper steel, which hadn't been heated high
enough for long enough to get rid of the impurities, and using thinner paint
coverings. The cheaper steel suffers from localised *internal* electrolytic
corrosion even when fully sealed from the elements, and was the main cause of
perforation at that time. I believe BMW at that time used to soak samples of
each delivery of steel in a brine bath for several hours if not days and if
any surface rust was visible at the end they would reject the whole
consignment. Things got so bad that eventually all manufacturers had to pull
their socks up and go for improved steel, better paint and wax treatments of
box-sections in order to offer multi-year anti-perforation guarantees, but
that was *only* against internal corrosion, not external from damaged paint
surfaces.
PaulH.
----- Original Message -----
I have seen the assertion that positive ground encourages rust, while
negative ground inhibits it.
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