Divide and conquer. Isolate circuits and check for drain. I am not sure if any fuses are not solenoid powered but you could pull fuses individually and check for drain. Always on radio memoryIJ
of course alt, and air heater or ether solenoid are in main curcuit. The curcuit breaker can fracture and short , the key switch can fail and partially energize the windings in the solenoid as well.