In addition to the above, remember that you do not have to have a "short" to blow a fuse... a place in the circuit which creates too much resistance ,like a corroded wire/connector/frame will cause excess electrical flow and blow a fuse. When groups (based on the electrical diagram) of things start acting up all at once then these common ground points are the first places to check. There might be , for instance, five main grounds between the motor/frame,battery/motor,instruments/frame.You don't really 'check them' .... you take them apart and clean them and see if that cures the problem.For real security in dirty places it is nice to solder even solderless connections , done properly it pretty much eliminates any place for water/salt etc to reside in a hidden place like the wire/connector. Another cause of corrosion is simply the placement of two different metals together,, and soldering keeps the oxidizing influences out of there (wires copper/connector steel,etc ). Remember also that we moderns use 'ground' and 'negaive' interchangeably even though some cars used positive ground ( MGB's with dreaded Lucas Electrics for one example).
Personally I think when they invented electricity they should have made it visible, that would eliminate much of my problems using it.
An alternator needs to be checked by a trained machine....it can only make a certain amount of electricity at any given rpm depending on how it is made... there is an inverse relationship between the amps and volts it can make ... maxed on one means low on the other....good luck, Greg