EGT installation, reading jumping around with 12v source

[mackdaddy240]

My egt has 3 wires, 1 illumination, 1 ground, and 1 power. I hook them up with 12v on power through my fuse box so it only comes on when the car is on and the temp gauge goes crazy.It seems to be reading my voltage because when I turn my headlights on my temp goes way up, same thing with windshield wipers and everything electrical. Is the red wire suposed to go to a constant .5 volt source or somthing? I have no instructions and its from japan.

[elvis240sx]

I was having a very similar problem. If my headlights were on, or the power seatbelts swung across, or even when my bass hit hard the EGT needle would spazz out and go nuts. I replaced the ground strap that goes from the left side of the head (left as in when sitting in the drivers seat) to the firewall. This completely solved the problem. That old braided steel strap was corroded and torn so I just used a piece of leftover ground wire from my amplifier. Hope this helps.

[mackdaddy240]

So your saying the braided seal for the hard wires that go to the exhaust manifold were screwed up? or the ground wire on the gauge?

[elvis240sx]

no, there should be a ground strap from your engine head to the firewall. It is usually braided steel. The EGT probe itself gets a ground through the engine I beleive, because once i replaced this ground strap, the problem cleared up completely.