How can you tell if a car audio capacitor is bad?

MystWlker asked the question:
Car audio system - 2 550 watt amplifiers, 2 10″ subs, 2 250 watt 6×9s, 1 .5 farad capacitor, upgraded battery and alternator. After installing the capacitor according to the manufacturer’s wiring diagram, I find that the car battery is draining while parked with the system turned off. The amps are powering [...]