The battery voltage is sensed at the SEN (J14 PinA1) connection on the interface board.
The charge current is sensed by the Current Sensor (CS). This sensor is mounted where the batterty cable enters the APU.
The sensed battery voltage is low enough to cause the alternator to be charging. The current sensor determines the alternator is not sending current to the truck batteries. TriPac shuts down to prevent discharged truck batteries.
Use an external amp clamp on the positive battery cable to verify actual amperage.
Refer to Alternator Diagnosis earlier in this section.