[smallblock450sl]

The JG5 number you found is the main wireharness part #. You have a G9-a. You should be able to find the cars serial# (from the driverside), look to the left of the battery, on the main frame, just below where the mid body hinges/tilts forward. There should be a brushed aluminum plate with the cars serial# and should start JG5-....... . Seems very strange it will turnover/start with a battery charger and not the "new" battery. I would use a volt meter on the battery and try to start it and see how low the voltage drops. If it drops below 10 volts the car would hesitate or not start at all. Good luck Dave