ok, I got an electrical water temp and oil pressure, the back lighs are hooked up to my dimmer switch. When they are lighted, the water temp reads 30deg higher and the oil about 15 psi lower(not all the time, and it increases like the car is overheating). When you dimmer the lights or turn the healights off, it reads right. I can't figure out why the gauges lighting would effect its reading. Any ideas??
Thanks

 

You must have the ground wire for the gauges connected to the variable dash light wire. Connect the gauges ground wire to chassis ground, and connect the wire going to the other side of the back lights to the gray variable instrument lights wire.

Tim

 

Tim,
I have had those gauges on for the last 2 1/2 years in the car, they never ever acted up like that befor. They started doing that about 2 weeks ago, for no reason...and both of them at the same time. It would be hard to think that both gauges went "bad" at once. Never the less, my ground wires are conneceted to the frame, and the lighting is from the fuse box.
Any other idea?

Thanks

 

If they used to work, look for a short or a broken wire.