Regarding rust perhaps someone with electrical background can shed some light.
As an apprentice before the advent of alternators most vehicles were Positive earth, it was not uncommon to see corrosion around the basttery terminal area, so now with Negative earthing I wonder if there is a connection (no pun intended) re Anodes ,Cathodes and car body rust?
Yes to some degree.
really with galvanic corrosion you don't even need the presence of electricity, if you have two dissimilar metals in electrical contact via an electrically conductive sollution, IE you have a stainless steel bolt and a mild steel body pannel, and that part of the car is covered in rain water that contains road salts and other contiminants, they the bolt and pannel don't even have to be touching, and the steel where ever water gets into touch actual metal, will corrode much quicker as a result of te galvanic reaction.
On big ships they install massive lumps of metal called galvanic anodes onto the hull, to focus the corrosion on the anode and save the metal. The metal will still rust a bit but nothing like the anode which will literally dissolve in the water.
The anode material is chosen based on the conditions. Ie most ships in the salty sea will use zinc or aluminum. In cleaner water areas like lakes and rivers you tend to use things like Magnesium,
Cars when made are Galvanic dipped, a kind of green coloured paint that contains zinc, but as per the chemistry the zinc in the paint is sacrificial and while it take the brunt of the corrosion over the steel it covers, given enough time and enough salt. the paint will eventually break down and let the water in, and is much worse with any little chip or ding in the paint that breaks the surface.
If you look at galvanic anodes used on ships, they are stuck over the paint. In the case of stainless steel, mild steel becomes the anode and will rust quicker.
That's why on modern cars aluminum parts can appear so covered in corrosion the alloy is a natural anode to the steel body.