6 amps current should get you by for basic testing and low power testing. I only use a 15 amp rated unit myself for everything except power testing amps to see if they perform to rated spec or not. 
PS set that supply at 14.4 volts which should the cold rated charging voltage of your vehicle. You can use 12 volts to imitate a battery type supply but when ever the motor is running the amp will likely see 13.85 to 14.4 volts Dc which is the charging range of your alternator system.
PS set that supply at 14.4 volts which should the cold rated charging voltage of your vehicle. You can use 12 volts to imitate a battery type supply but when ever the motor is running the amp will likely see 13.85 to 14.4 volts Dc which is the charging range of your alternator system.