Ground location for boost controller and gauges?

SouthArk370Z

If the black wire under the bolt near the center of the picture is factory wiring, that should be a good round. If it goes to something that you installed and the device works, it's probably a good ground. Either way, I'd give it a try. Measure resistance from the bolt to the negative post on the battery (or a known good ground). If very close to zero, you should be good to go.

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