coil polarity

[RDfella]

For those who run ignition coils, thought the attached might be of interest. Came across it in a classic car magazine I subscribe to. I always believed that when changing a vehicle's polarity, the coil's leads should be changed too - ie coil +ve should go to battery +ve. But apparently not always ......

[Swarfcut]

 Interesting concept there RD. I've always fitted them SW/CB regardless of the battery polarity. But yes, aftermarket ones marked + & - are questionable.  Specific model replacements usually have different size terminals to ensure they fit the right way round.

 As for vehicle polarity my Dad told me the corrosion of steel bodies was less with negative  earth systems compared to positive earth, supposedly discovered in the early days of unitary construction. More like makers hype? How come you never see a vehicle with a sacrificial anode as in marine practice? There's no shortage of salt water on UK roads in winter.

 Swarfy.

[Triton Thrasher]

Tell the corrosion prevention story to my 1967 negative earth Vauxhall.

I heard that sacrificial anodes are not applicable to motor vehicle bodies because the vehicles are not submerged.  Could that be right?

[Bsareg]

To be effective the water (electrolyte) must be in contact with the metals to be protected and the noble metal (normaly Zinc) which is the anode, difficult on a car. Although, I have heard that some pre-war manufacturers used Zinc washers on aluminium bodies where they are attached to the steel chassis.