Will old wiring work with HO alternators?

My 1982 POS Dodge D 50 came with a really low output amp. I replaced it with a 45 Amp alternator. My headlights are still dim. I got an H4 kit - still dim, but more illuminous. I also have 5 6" KC's and 2 4" lights by the grille. There's an 800W stereo system inside, also. Well, I tried installing a second battery - now it's a little better, but I can't run TWO KC lights and the stereo without my capacitor screaming at me. I'm gonna have to get another alternator - leaning towards a 100Amp I located, but will the wiring be able to handle it? I have seen some 220A beasts - but I think that would be overkill. Any advice/tech tips are appreciated!!!