According to the manual that came with my Vanner Eq, you should never connect anything to the Vanner except the battery. All loads (12 and 24 volt) as well as chargers connect directly to the batteries. The Vanner doesn't supply 12 volts; it just brings the low battery (one supplying 12 volts) back up and keeps the high battery from over charging. The 24 V terminal connects to the high positive post, the 12 V terminal goes to the terminals where the batteries hook together, and the GND terminal connects to the negative that's the chassis ground. Go to www.vanner.com
and you should be able to find specs, hookup diagrams, and general info on it. Good luck!