The run position shows start system voltage when engine is running. The other three positions are for start batteries, house batteries and the aux is for the bank of batteries I have for computer batteries. When the engine is not running the panel is off until you push the button below the meter. When engine is running, with the switch in the run position the meter is on all of the time. You can also check the other banks while engine is running by switching to the appropriate bank and pushing the button.
I built this junction block to be installed in the wiring junction box accessible from the outside under driver side window. It will keep the strain of big wires off of the back of the meter/switch assembly.