My DiPricol EGT gauge has no 12v power except for the lights, so turning on the ignition does not affect the reading at all.
I thought all the EGT gauges (except for the digitals) worked this way, but probably thought wrong, for the first time in my life, LOL.
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1996 3500 Clubcab SLT, auto, 4. 10 limited-slip, TST #5, 370s, AFC spring kit, Psychotty, Dunrite converter, Trans-Go, Walker 21471, DiPricol EGT, boost & trans temp. gauges, 9 ft. aluminum flatbed and tool boxes with Venco dump. Custom front bumper, Hadley air horn, PowerVision mirrors.