[joyridin']

You have something else going on there. 8 gage wire is fine, so that isn't the issue. If you are getting only 11-12 volts on the meter, then your alternator is bad or your battery is toast. We will rule out the battery since you can start the car without a problem, but it might not be a bad idea to do a load check on it.

You do not mention the pulley ratios. Is it possible the alternator is not turning fast enough when you drive? What happens when you rev the engine? Does the voltage go up?