Charging questions

Without knowing more about your fan setup, it would be only a guess as to a switch. There's a relay you say, so put a switch in the fan trigger line.

Please read the MAD article which has a very good writeup on the problems with factory wiring and oversize alternators

EDIT the website seems to be down. Google "Mad electrical" and look for the article on bypassing ammeters.

The main problems are the poor terminals in the bulkhead connector, the possible failure of the ammeter and ammeter terminals, and generally too-small wire for very large alternators.