volts are surging alternator goin?
If the volts are surging high, over 14 volts, then that's most likely a loose ground wire connection. If the volt gauge is just moving up and down that can be normal depending on what engine rpm is and what accessories you're turning on and off such as headlights and heat/ac. With an underdrive pulley, you're alternator will spin slower at idle so it will be normal to see lower voltage at low rpms and normal to see the volt gauge move more as rpms rise from idle. And it can also be a bad diode in the alternator causing lower output in which case the alternator could be on it's way out and needs replacing or at least a new rectifier.

