if your trucks wiring is in good condition and not a rats nest from 50 years of previous owners messing with it, all you need to do is replace the alternator, you don't need to add anything, particularly not something you don't understand - if the wiring is a mess replacing the complete harness is your best insurance against a future electrical fire ... most vendors have a complete reproduction harness with the alternator upgrade for around $200, 400 is way too much
the original generator on your truck with a V8 would have been 45amp, sized to deal with every available electrical accessory operating at the same time [wipers, heater, radio and all lighting including clearance lights, foglights and a spotlight].... a 100 amp is very much overkill, useful only if you plan on electric fans on the rad, high power halogen lights, power windows, AC, a stereo amp big enough to break windows, etc etc
the highest reading of the ammeter will be just after you start the truck and the charging system [generator or alternator] is replacing the drain from the battery ... the highest output alternator you can get doesn't change that, although some will say that alternators can surge at first until their regulation kicks in - I've never seen that with the vehicles I've put alternators of 65-85 amps on ... fix what's broken now, make sure the wiring is in good condition, especially all connections clean and tight, and start learning about how the electrical system works so you can recognize future problems as they arise
Bill
