My 65 El Camino charges 14v while driving but when I let the car sit overnight my voltmeter only reads 10v.When i jump it all it takes is a second and the car fires up,I changed the battery thinking it wasnt holding a charge but that wasnt the problem.I have an internally regulated alternator and a high torque starter that are about 6 months old.If I turn on/off the engine all day long while driving around town it has no problems starting.Something is drawing power while the car sits for a period of time could it be a switch in the car.This problem started to happen more frequently as of late.What is the easiest way to diagnose this problem.
Thanks
Brian

With everything off in the car (aftermarket radio memory, clock, door switched dome light, etc) hook a voltmeter up between the battery's positive post and that battery cable. Note voltage displayed. Then one by one, remove the fuses in the fuse panel. When voltage displayed on the meter drops to near zero, that is the circuit with the short.