Hey Scotty, I have a 1993 K1500 4.3L 4WD Pickup. When I turn the heater on high and switch the lights on brights or turn a blinker on, the check gauge light flickers on in unison with the blinker. The oil pressure is reading correctly. All other gauges are reading what factory specs say. Any ideas what it could be? The battery gauge moves back and fourth quite a bit when the blinker is turned on as well. Could it be a bad ground to the gauges? If so where and what ones? Thanks

first , go to auto zone, they load test batteries and alternators free. My guess is bad alternator, but if not that, then wiring is bad somewhere and GMs are known for bad ground wiring when that old. good luck