I'll call that wire A (it's confusing to describe in words). A is connected to the closed post of the ignition switch in the panel and to the + wire (brown) of the regulator harness.

The wire that energizes the ignition panel I'll call B, comes from the + post of the starter where it's terminal meets the battery cable to the starting battery. B then connects(via a split terminal connector at the + post on the starter) to one output post of the dual output balmar.

Because that wire carries the full charging output of the alternator back to the battery(where they meet back at the + terminal on the starter), B I think is 10ga or larger(I'm not on the boat).

I installed A with 12 ga(wire B is original to a previous high output alternator) as I thought I would keep it the same as all the + 12 ga. line through the ignition panel that energizes the meters, gauges, etc in the panel.

For all wiring from where A meets B at the ignition switch, I'm thinking a panel fuse holder installed before the switch with a 20amp fuse will now protect A and the other + 12ga wires down current in the panel. This seems handy and fast. No ignition?, unscrew fuse to check.

This of course doesn't protect B which would require a heavier fuse or breaker inline just after it's connection at the + post of the starter. What's the correct thing there?

If this isn't too confusing, am I thinking correctly?

The regulator has an inline fuse just off the sense wire as you probably know. I suppose this is factory installed to protect the regulator from an overload from the alternator.

Thanks for any help.