Instrument panel ground location

[justbinfishin]

Hi all, two of my gauges (oil and temp) go up considerably when I hit the brakes, turn on the headlights, blinkers, crank up the stereo or do anything with significant electrical draw. During daylight hours, the temp hovers over the "o" in Normal but goes up to the border of A and L when I turn on the headlights. I am fairly certain it's a bad ground in the instrument panel, and I'm curious as to the location and difficulty of reaching it. If you think I'm wrong about the diagnosis, what do you think it is and how would I go about fixing it?

Truck info is in my profile info to the left.

Thank you!

 

[rtg143]

They both use different ground wires at the cluster, but ground at the same point behind the right kick panel.