I dont really know about watts and amps all so i just wanna make sure?Here is what i have:
1)a 400 watt amp
2)140 watt cd player
3) a low drain blacklight(not sure what the watts or whatever are)

I have a 85 firebird with the original alternator.
Thanks

 

Well it looks like you have the stock 90 amp alternator. That will shortly die just b/c of age not b/c you are overloading it. My stock alternator in my '86 Firebird went out last month and I was running a 140 watt Clarion deck, a 600watt RMS amp and 2 10's and some high *** powered 6x9's and my alternator which was a stock 90amp held up just fine for 1.5 years until it finally gave out. Now I have a 110 amp b/c that is what the stock size went up to, which is cool

- Mike Harvey -

 

I = P/V, so I = (400 + 140) watts / 13.8 volts = 39 amperes. Also, conversion efficiency must be accounted for, so 39 amperes / 80% = 49 amperes at full output. The amplifiers will probably not be run at a steady state full output though, so the nominal average current draw should be much lower. Also, the battery will supplement a short duration peak current draw that exceeds the capacity of the alternator, however, the system voltage will dip to a "brown out" condition for that short period of time.

Tim