Dude, are you sure you were measuring ampiers? An amp is a unit of measure for current (1 amp flows through 1 ohm of resistance when 1 volt is supplied). What you should be measuring for alternator output is volts. If you're putting out 18-19 volts, it's no wonder your car's not running right. A properly working alternator should put out between 13.8-14.6 volts DC. If you're measureing current draw from the alternator, something's wrong as well, because there should be way more than a 18 amp draw when the motor is running.