Stop in for a cup of coffee

Grou
Got a question for the Coffee Crew, the wife’s 2001 Ram 1500 4x4 5.9 Magnum periodically when outside temps get hot and she turns on a/c the dash warning lights come on and all gauges including speedo stop working. Truck runs fine and the air works I believe, not for sure on that because she has shut off the air immediately each time. No working gauges and warning lights on freak her out. (Not a bad thing in my book)
Any thoughts?
Bad ground.