[Fw190d9]

I dont have the wiring diagram around but basically, its a big solenoid that is hooked up to the main battery on one side and the aux battery on the other. A small circuit board attached to the solenoid senses output from the alternator and battery voltage on both batteries. It will send charging current to the main battery first, then once it shows charged, it will charge the aux battery also. It also has a function that connects both batteries together when starting to get max voltage only if both show an acceptable charge. You can drain the aux battery with accessories like winch, stereo etc, and the main battery will stay fully charged and still allow you to start. Seems to work pretty well so far.

Evan Q.