A warning for all pre war owners.....

[Sydsmith]

Hmm, we are getting way off topic here and going back to Jed's point, I had a Morris 8 years ago that suffered the same issue, the rubber around the main cable perished inside the flexible conduit covering and became sort of crystallised, when wet it was mildly conductive and smouldered, in the end I had to replace with modern cable.

But to take up Peters point about the polarity change, I was a radio engineer and car radio fitter at that time and it did more or less coincide with the advent of transistorised in car equipment, but it is possible to opperate transitors in bot negative and positive earth circuits and because there was a mixture of both neg and pos cars about, most radios I fitted at the time had polarity change facilities and could be used on either so I doubt that was the reason for the change.

We were told at the time it was to reduce battery post corrosion and as has been said body rust, but I am not sure of the chemistry. Syd

[Stan Thomas]

Change of polarity was mainly to do with body corrosion - because in simple terms it was a car!!

You see, rushing through the air produces static electricity, which promotes an electolytic action to combines steel with oxygen to produce ferous oxide - commonly known as rust, and it was considered "positive earth" reduced the effect.

Same thing happens with ships, which is why they have "sacrificial" elements on the props and hull which more readily accept the corrosion, and millitary vehicles often have a skate touching the road surface to ground the static.

Unfortunately for us landlubbers though the "sacrificial" element would be the least insulated part of the metal bodywork - which is why a body repair will begin to rust quicker if not properly sealed and painted.

P.S.
SP Owners can disregard the above.

[John Hitchins]

I remember my family DB18 had a bath chain dangling on the road as did many cars in the fifties. I was told to aid travel sickness but probably nonsense.