Switch question

Here is a rotary switch that looks like it will do what you want. Not cheap, though.

For the price of the switch, you can get the ZW meter from Lionel.

Larry

Are you metering voltage or current?

If you are measuring voltage, you only need to switch the "hot" side since all of the Commons are tied together inside the ZW.

You want "non-shorting" contacts.

I would try surplus places.  All Electronics has a 7-position switch for $2.50, but it may be a bit difficult to add wire leads to the PC board pins - http://www.allelectronics.com/...rotary-switch/1.html .  If you were to use small-gauge wire (since the wiring doesn't carry much current for a voltmeter), you would minimized the strain on the terminals.

If you are measuring just voltage as alluded to in your diagram(no load connected to the meter), you need a SP3T switch(could be toggle, rotary, slide, rocker, whatever you prefer, has 4 terminals/connections).

You may have more of a choice in switches if you source a DPDT on-on-on switch, which by adding one jumper on the back of the switch becomes a SP3T.

There would be no need to switch the "U" posts, they are common.

As Dale points to, you would want a break-before-make switch design to eliminate fault currents/shorts across the ZW secondary.