alternator wiring upgrade help

I have a 1991 nissan sentra . it has a stock 70 amps hitachi alternator . i have upgraded my music but now the lights dim. i don't have a capacitor yet . i have upgraded the wire from that neg. pole of the battery to the body with a 4 guage wire and now the lights dim much less. i aso want to upgrade the wire from the output of my alt. to the pos. pole of the battery . i have traced the output wire from the alt. and it goes to a box of relays and then dissapears close to the head light and then appears running under the frame by the radiator. then comes to the battery pole. i have checked for continuity on that wire and it is the same wire but i'm not too sure if it goes through any relay(s) or any circuit.
What i want to do is run a 4 guage from the output of my alternator directly to the battery . If i do this , when my engine is off will the battery discharge through the alternator windings and or brushes ?Do i need a high current relay to interface this wire ? will it harm any circuit or electronics in my car ? Any help will be appreciated.....

-------------
"I'm So Loud It Hertz"

you dont have to worry about anything, just do exactly what you were thinking and run the wire directly from the alternators charging lead to your positive battery terminal...there will be no harm to anything this way...

on a side note, dont waste your money on a cap, save a bit more and buy a high output alternator...you will be way further ahead in the long and short run...

Big Purds is right. you can run it from the alternator right to the battery with no problem. by you doing what you have just described will cut down the dim lights some, but not all. with the bigger power and ground, more current will flow. if you do choose to put on a capacitor, stick with a 1farad or larger. mount it in line close to your amp or right off the distrubution block. this should cure the problem. but on the other hand, your factory alternator can only take so much. so the question is, how much power are you running or wanting to run in the future? if what you have right now is what makes you happy, buy the capacitor. but if you want something bigger and better save your money and invest in a good alternator that will hold up and solve your dimming lights for good. hope that this helps too.

-------------
JC