electrical temp gauge issue

[joe440]

So i have the sending unit wire going from the trans line where i put the T fitting in, up to the gauge and wired to "sending unit" stud

I wired the ground to an existing good ground.

Now all i thought was i had to wire the positive into an existing power wire to another gauge or right into the fuse panel because i have room to put one in there.

Once i have it all connected and turn the car on, the gauge jumps all the way up to hottest number on the gauge. (I know for certain the tranny is not that hot)

I tried disconnecting the sending unit wire and left the ground and positive on and it does the same thing.

Any ideas? Thanks

[astroracer]

The sending unit is probably not getting a good ground. How do you have that installed?
Mark

[Ron.in.SoCal]

Pretty sure Astro is right. It's a ground somewhere. Just went through this same problem last weekend.

[Supra510]

Sender grounded?

[joe440]

The sending unit wire came with a little fish eye that is crimped on and tightened down with the nut that's shown in the pic. That wire just goes up to the back of the gauge and connected to the sending unit post. Then the ground post is wired to the firewall with a previous good ground. And the positive is wired in sync with the volt meter positive post.
https://static1.pt-content.com/images/pt/2013/08/null_zpsde3bc1b4-1.jpg

[Schwartz Performance]

The sending unit itself needs to be grounded. That means a wire from the npt threads on the sender to a good ground.
-Dale

[joe440]

Just tried that, still jumps all the way up.

[Red67Mustang]

These work by varying resistance to ground. In the gauge pegs then you have an open circuit or a short to ground (depending on which way the gauge is designed). Time to check the wiring. Disconnect the sending unit entirely and power the gauge to see how it behaves then. With KOEO ground the sending unit wire to a chassis ground and check gauge behavior. Could be a bad sending unit.