referring to fig7 the load management system 50 includes a power on permissive switch circuit 60 which when actuated by power from the vehicle ignition key k through typically an indictor light l to terminal t5 provides power from the battery to the integrated circuit ic1 and to the precision voltage reference circuit 70 the lead 61 also bypasses power from the key switch k to the field through terminal t7 for the 34 start 34 circuit 54 described above a vacuum switch 80 that senses manifold vacuum from the vehicle 39 s engine e not shown in fig7 applies battery voltage to the high low shut down pin 10 of ic1 in other words when engine vacuum is low due to a heavy load the voltage on pin 10 is low and turns on ic1 to activate the load management system 50 as will be described in more detail below when vacuum is high indicating only light or no load on the engine the vacuum switch 80 turns off the battery voltage so that pin 10 goes high and shuts down ic1 thus allowing the alternator to operate and charge in a normal manner high vacuum also applies battery voltage to the 34 start 34 circuit 54 through terminal t7 to be sure the.