1...Upgrade factory wiring. At minimum, do some sort of upgrade to the main charging line, consider bypassing the ammeter.
2...For darn sure add a second fuse panel. Feed it completely separate with oversize wire
3...Add a minimum of 2 switched relays, 1 to power the existing ignition circuit under the hood "ignition run" and one to switch off the original accessory circuit. That relay can "key" the added stuff without loading the original
4...Think carefully about fuses. You want them to protect the WIRE and you want them as CLOSE to the source of power as possible.
5...For sure upgrade the alternator, see 1 above
6...I would ignore the statement "don't power direct off the battery." After upgrading the alternator and associated wiring the battery is EXACTLY where you want to source the power
When an alternator is PROPERLY wired, NOT like the original, that wiring is no longer an issue. But the battery acts in some ways like a filter and is much less "noisy" (RF/ EMI issues) than the alternator output.
Alternator output wiring, especially when adding "more stuff", pumps, fans, big stero, etc, needs to be OVER sized 60-80A? I'd run about no6 wire to battery. If you don't have / can't get some, parallel, 2 or more no 10 wires
Here's a MARINE amp/ capacity chart. Remember, the distance figure is "round trip" as in a wood/ glass boat no ground return. So the 10' distance example is same as 5' of wire in your auto
Marine Wire Size and Ampacity | West Marine
View attachment 1715520681
