Heres a picture from an old layout showing the wiring on the rear of a 3 power district meter panel. Colored wires are the Hot wire runs from 3 separate PoHo transformers to the ammeters on the bottom row. Note the Hot wires connect the ammeters inline(in series thru the meters) and return to the load (the center track rails) The white wire connected to the 3 volt meters is the Common (combined common from the 3 phased PoHos and is also extended to the outer rails). It connects across the line (in parallel) and jumpers power to the volt meters on the top row. To complete the across the line, Hot to Common, connection of the Volt meters one can see the short HOT jumpers extended up from the ammeter terminals. The hot wires must be a heavy gauge wire since the full load runs thru the ammeters. If you are using Command Control the volt meters will show a steady 18 volts. The ammeters will reflect the railpower load of the locomotives plus car lighting.
In this case the Volt Meters used were 0-25 VAC and the Ammeters are 0-15 AAC. Hope this helps.
