Alternator 100 amp

I'm doing a swap and I'm not sure if can run a 100 amp alternator with the original main fuse of 80 amp?

It depends on exactly how the wiring harness has been wired, but you will probably be fine. Don't forget to up-spec the alternator ground wire, if used.

Like Gord said if the full 100 amp potential wouldn't run through that 80 amp anyway, it's not an issue.

If, however 100 amps could go through the 80 amp fuse during normal service, then yes I'd say it should be uprated well beyond the 100 amps, along with the wiring.

I should have asked, what vehicle is it? Many/most run the alternator output directly to the battery, to the starter main feed, or some other common point and not through the fuse-box/a fuseable link.

However, some do, and that's where the fun starts.

The other thing to remember - sorry if it's granny-eggs - is that's the maximum potential output of the alrternator. Under lower rpm it won't be producing that much, and when it is out-puting it will only be what's required to balance the electrical load and keep the battery charged. They're basically voltage regulated - putting out enough current to maintain a minimum voltage, usually 13.8-14.4V.