Use these testers to determine if a 12 or 24v cable or port is working correctly. A solid green light means the cable is good. An intermittent or flickering light means the cable needs repair. A RED light means the polarity is REVERSED. Panavision uses reverse polarity for 24v power supplies and batteries so the 24v tester will display the red light when used with Panavision gear. This is useful when mixing personal 24v and Panavision 24v gear. The 24v tester is 3 pin. The 12v tester is 4 pin.