Thanks for adding your chassis info .
As ; sledhead ; stated in his post , it appears the dash lights and gauges are fighting to find good ground , so locating and cleaning the ground for the dash wiring harness would be the first thing to do.
There may even be a ground on the instrument cluster printed circuit board that requires attention.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.