Quick Autometer voltmeter wiring question..

[FiveLiterFox]

I'm installing a series of gauges below the radio, one of them being a voltmeter. Autometer instructions state to run a 12V switched source as well as a "good engine ground."

Is an "engine ground" really necessary? I would think running the ground to the chassis (ie; the steel dash reinforcement) would be acceptable? Is there any reason an actual engine ground would be necessary?

[Supercrewzer]

i ran my ground to metal on the kickpanel underneath the dash. works fine, i get a solid reading