First of all, it aint me!
My next door neighbour "was" selling his Cav tomorrow, after removing the original battery, he put in a new one to goto the new owner.
Unfortunately, this one decided that it would change the +/- location compared to the original one.
A few sparks flew, and we then realised what had happened. He went to put the original battery back on and the same sparks but worse were appearing.
He then stuck the key in the ignition, and all lights came up on the dash, but then smoke came from under the hood.
We think its the alternat(or/er) but he needs to know what else could of been damaged in the result.