Thanks Maine Sail. I just stopped by the boat, and found some interesting details:
First, the current alternator "out" wire appears to be a #10 AWG, and it wraps around the block, and then connects to the starter solenoid. From the starter solenoid, there's a 1 AWG cable that goes to the battery switch on the center post.
Typical factory installation..
Is there any good reason why the alternator would go through the solenoid, or was this more likely a matter of convenience with the wiring harness?
Only that it is cheap and easy for the manufacturer and when boats came with only two batteries and a 1/2/BOTH/OFF it allowed the user to select where the charge current went. Bottom line it is cheap and easy and builders still do that to this day.
Second, my alternator is only 75 amp, not 90. Though by Blue Sea chart, that's on the line between 4 AWG and 6 AWG, so might as well go with 4.
The only thing that hurts by going bigger is the wallet..
Third, I can't find a ground wire attached to the alternator that runs back to the ground. I can find a couple wires that supply ground to other things like gauges and the voltage regulator, but it appears that the Balmar is grounded by its mounts. Is this even possible?
Some older Balmar's had a case ground option but most still shipped with a ground stud.. If there is a ground stud on the back of the case make good use of it....