I have a 1999 Jimmy that has me scratching my head. Every time you turn the HVAC to anything but off, the warning lights and digital odometer shut off. When you switch back to off on the HVAC, the odometer reappears and all the warning gauge lights turn on as if you just turned on the ignition switch. Could this be an ignition switch problem or could it be the HVAC control head? Thanks to anyone that can shed me some light on my problem.

It's either the control head or it's a bad ground.

Just an update for anyone having the same problems. It was the ignition switch. Had it replaced and everything works normal now.