Converted to alternator years ago. When I turn the ignition key on the red dash light does not come on. The voltmeter gauge often does not go beyond 12/13 volts. I took a long drive today with no issues. Parked the car for about 2 hours. Went to start the car and got nothing when I turned the key on? Boosted the battery and ithe motor started and the gauge showed it was charging? Any thoughts on this?