Severe voltmeter needle oscillations

Cuda416 said

This sort of illustrates what I am referring to. Imagine the open end points are where the battery is. The "V" is your meter with leads across the fuse box in parallel with other loads. The "switch" represents your turn signal. Once that switch/signal is closed, there is zero load across the v-meter leads and so zero voltage drop (difference of potential) and no reading.

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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