Magnum Alternator Wiring
I would not use more than 45-50A at most on a stock harness, bear in mind these are old and could be already damaged. In no particular order, every wire end, the wire size itself, most especially the bulkhead connector terminals, and the ammeter and it's connections
If you cannot do anything else, just get a fuse link/ breaker/ fuse and put a nice big no8 or larger wire from the battery to the alternator. You DO want to fuse this.