we had similar problems with our Ford Explorer toad, so when we upgraded
to the Jeep Grand Cherokee I changed from a 4-wire cable to a 7-wire cable. Then we installed a separate constant-duty solenoid and high amperage fuse in the main electric control panel near the batteries. The 12VDC wire in the 7-wire cable was fed by the constant-dutye solenoid any time the DP engine was running. As a result the Jeep's battery was being charged directly by the Cummins any time the Cummins was running. When the Cummins was off, the solenoid was off disconnecting the 12VDC lead to the Jeep preventing the Jeep from draining the DP's chassis batteries.