Hello everybody I'm new here but I have a question.

I have a 91 Camaro 1LE Z-28,
The car has Full MSD ignition, underdrive pulley, Autostart, alarm, aftermarket fuel pump. This is the way I bought the car, the last owner said it needed a batt, and alt.
I replaced those and went threw 3 alts, thinking they were the problem.
The car charges at about 11volts, small variation with rev.
if you turn the A/c on it dropps after 5 sec to about 8volts.
if you turn the a/c off it goes to about 10volts.
turn the headlights on it goes to about 14 volts.
with all this the tach bounces alot like a loose connection
This is the wierdest thing i've ever seen, and help?

 

try checking ur fuses, then ur ground connection. lastly to check ur alternator if u don't have a volt meter have the car running, disconnect the negative ground wire from ur battery...if it cuts off then ur alt. isn't charging ur battery. keep me posted.