Severe voltmeter needle oscillations

67Dart273 said

Somehow I got lost in all this. Are you suggesting he connected the neg side of the voltmeter to a LOAD instead of a GROUND?

That makes perfect sense. The neg side of the voltmeter MUST be PERMANENTLY grounded, and not plugged into something that can be live at times.

Also the voltmeter needs to go to a key switched source --otherwise it will drain the battery eventually

Click to expand...

Sort of. The leads need to be across something that

1. Causes a voltage drop
2. Doesn't have any intermittent bypass.

If you look at the diagram, when the "switch" is open, then the leads measure the drop across the load. When the switch is closed, then the easiest path is through the switch an there will be NO drop across the load because of the short that will bypass it. In that diagram, when the switch is closed, the voltmeter will read zero. This might explain the extreme fluctuation of the meter he's seeing.