instrument grounds

[Ozzie Goat]

I have intermittent problems with the gauges changing when the headlights are turned on. A new ground from the battery to the frame helped a lot.

I'd like to add one more ground to the instruments.

I plan to add a wire from the voltmeter to ground in order to have two ground paths for the instruments circuit.
Rewiring all of the instruments to individual ground circuits might be optimal, but that's too big of scale for me on my back.

Question: The volt meter has one green wire (power) and two black wires on the other side. Are these two wires the ground ?? Does what I'm describing make sense to alleviate problems related to the daisy chain for instrument ground??

Thanks