On my '89,with a cold crank and sometimes while still warm,The volt gauge jumps and the engine runs kinda rough,i give it gas,and it straightens out. Could it be the battery not giving enough charge cuz when i turn the A/C on full blast,it takes a chunk out of my voltage accroding to the guage that is and you can feel a small jump in the engine,although that could be the clutch kicking in. Or could it be a bad ground?
Thanks.

 

There are more than a few possibilities that come to mind when voltage drops off at the gauge under load.

1.) Frame/body ground straps making poor connection.
2.) Main Battery ground cable has poor connections at the engine, body and or battery.
3.) The Positive Cable is corroded at either end.
4.) The power leads to the positive side of the battery from the alternator are either corroded or heat resistive (burned once and get resistive)
5.) Weak or bad diode in the rectifier inside the alternator. Remember that all the power you use comes from the battery and it's the alternator's job to refill it.
6.) Weak or bad cell in the battery itself.

remedies

1.) break out a wire brush and clean ALL ground and positive power connections between the body / frame / battery. This includes all the frame to body straps, frame to engine straps, body to engine straps, both battery cables (4 connections for the positive side and 3 connections for the ground side).

2.) clean all alternator connections.

3.) LOAD TEST (not just with headlights and heater on full blast) with a carbon pile or similar testing equipment, the alternator for weak diodes, weak or bad voltage regulator, weak or bad windings.

4.) LOAD TEST (AFTER charging all night) the battery with a carbon pile to rule out weak cell, shorted plates, open cell(s)

I'm betting on poor connections at this point. All of the above should take the better part of an afternoon, so make sure it's on a day where your parts store is open late.

Larry