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Gentlemen-
My port Crusader 454 engine has 2 leads from the alternator + (Prestolite 12v 51a) an orange wire (#10?) leads through the engine harness to the + side of the starter and a red wire (#10-#12?) leads about 8 feet away to the alt on the isolator and a #6 wire leads from the isolator to the house battery switch. I believe I should be using #6 for anything that might be carrying 50 amps. I know the alt is not producing peak numbers at normal operating RPM. I just want to do this right. So, am I way undersized on these alternator leads? Looks like they have been this way for a while... don't mean to infer it's right just wonderin'.
Thank you,
Stephan

If you go by the numbers a #6 is correct.

But almost every wiring harnass with a 35 to 55 amp altenator uses a 12 or 10 wire back to the starter battery terminal because its a short run and the chance you'll see 60 % of the alternator rating is slim enough not to warrant the larger wire size.

The longer the run however also dictates wire size so you don't introduce resistance into the equasion.

BTW that isolator is dropping the voltage about .6 to .8 of a volt pushing it thru the diodes so while it will somewhat charge a battery like that, it will never charge to peak and standard lead acid will end up giving a shorter life cycle as the plates have a better chance of sulfating if that is the only charging source.

I much prefer to control charging thru the use of the battery switches, mechanical not electrical.

1. It forces one to open the engine hatches and observe while turning the switches.

2. You get the max output.

This also goes for the battery parallel circuit. Much rather deal with the actual switches because many times the battery working the solenoid is the one dead. Many do not have dual or triple feeds of all batteries that have to be run thru diodes to prevent inter connection of the batteries thru the parallel circuit.

I've seen numerous occasions where the parallel circuit was burned up because start current was path'ed thru the #14 wires because no isolating diodes were used and again with the use of diodes voltage drops. Some solenoids can be affected by that also.