Going down the road my tach works when it wants to. Push in on the top right hand corner of instrument panel and it starts working. Took out the entire instrument panel and put another one in. The tach, oil pressure,and voltage will stop working when I turn on the headligts or the dome light. The four light bulbs around the tach are very dim.Had same problem with old instrument panel. Discovered circut board on back had a break in it. When repaired everything worked fine. The new one is in excellant shape. Why do they stop working when I turn on the lights? 86 camaro v8 305 tuned port

Sounds like a bad/loose/dirty ground somewhere in this circuit. When the lights are turned on, the current demand is much higher.

Joe

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69 396 w/SS Trim, B&M TH400, 3.55 12 Bolt Posi, Blue w/White Z28 Stripes, Chrome Rally Wheels
Badboatdude@CS.com
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i have had the exact same problem with my 85. check the grounds first (i think theres 3 total for the instrument cluster) and check the connectors behind the instruments. the connectors have to be snapped into the dash before the instrument panel is installed. it sounds to me like they may not be snapped in all the way.