Excellent advice. I had kind of decided that on my own when you pointed out my lack of knowledge on getting 120 out of it.  The system currently has an analog meter that failed, so I have the existing leads to tap into for measuring the voltage.  What I think I will do is just use a battery with a push-button switch.  When I want to know the voltage just push the button.  Sound reasonable?

Reckon 3 AA or C batteries will get me close enough to 5VDC or do I need to use 4 or a single 9V and regulate it down to 5?