I want to use one panel mount voltmeter (Powerwerx PanelDVM) for measuring both my 12VDC Battery output and the input voltage from a Solar panel ,which has a higher DC Voltage. This all is hooked to a battery charge controller (shown below). I will be using a SPDT switch (on-off-on) to switch between voltages and would hook both the solar and battery grounds together at the switch, but I am not sure if this would cause a issue. Such as: damage to the solar panel. It may be better to buy 2 voltmeters
update: I agree with everyone that said: "Use a DPDT Switch". I only went this route because I had a hard time finding a round, center off, Panel mount, DPDT switch, but it really isn't worth risking damage to the Solar panel.