It is probably easier to re-wire the cart for a positive key switch.
Disconnect the 2 wires from the key switch and splice them together.
Run 2 new wires from the key switch to the FNR switch.
Disconnect the red wire from the FNR that goes to the VGlide micro-switch.
Connect one of the wires from the Key Switch to where that wire was connected.
This will be the "Hot Side" or the always ON side of the key switch.
Connect the other wire from the key-switch to the wire that goes to the VGlide, that will be the "Cold Side" or the side of the Key Switch that only gets power when the switch is ON.
You can now wire any accessories: Voltmeter or Converter to your new positive key switch.
Use different color wires (or tape the ends of the wires with different colored tape) for easy identification.
Use the diagram below for reference:
