when galvanised if the steel is exposed [ie by drilling or scratching] the surrounding zinc forms a galvanic cell and protects the steel - an example of a sacrificial coating because eventually the zinc is erroded away.
This is an area I scratched the surface of (not intended) when I got my first Morgan which was a +8 this had been fitted with stainless firewall and inner wings retrospectively. I know enough about the Cathodic table to know that alluminium wings and stainless inner wings will eat each other electrically unless there is a complete barrier between them. You see these metals are about as far apart from each other as you can go on the Cathodic scale. Add a bit of road salt and H2o and errosion begins on a grand scale !
This link will provide a little light reading for you all.
http://www.corrosionist.com/Galvanic_Corrosion.htmIt won't stop me enjoying mine though just as HFS and his descendents intended. Pictures of the early "properly" Lands End trials makes you realise this is what they had in mind when they built them - not polishing - sorry Dave with your concours bonnet on !
