Dash gauges dont work with headlights on

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I have a 1995 Chevy Tahoe in my shop and when ever you turn the headlights and scroll the dimmer wheel the gauges all gradually stop working. For instance if the more you scroll the dimmer the closer the gauges are to hitting the zero mark on all of them. I have already replaced the dimmer switch. It didn't change anything. Seems like there is a short somewhere most likely. Any Suggestions? Thanks in advance.