See the attached jpeg which shows how I wired it. Seems I am
doing something wrong. I got the Sure-brand DPM 0-20 V from a Hong
Kong vendor, and I downloaded the linked .PDF on the pinout, but
something is wrong. No, I am not trying to read the 5volt output of
the regulator that is powering the DPM, I am trying to monitor the 12
V battery voltage that is supplying power to the 7805. I don't know
if this means I am still trying to monitor an "unisolated" voltage and
thus screwing it up. It doesn't seem that it is damaged in any way---
when I touch what I THINK should be the input sig. + to either the 12v
battery powering the regulator, or to a definitely isolated 9V
battery, the DPM flashes normal-looking 4-digit voltages for a second,
and then after that just shows the over-range indication. It never
flashes the same voltage, when connecting repeatedly, it appears to
be random. It also never shows the correct 12v or 9V. With no input
sig. the DPM shows NOTHING at all....but I don't see how this could
actually be the DC voltage input wire, as I would have fried the unit,
surely. It could be I got a defective unit just like the batch of
7805s that I got putting out 7 volts. I ordered another identical DPM.
thanks!