Weak Grounding problem with Temperature sensor

[Ivan141]

You could try finding the ground wire that is originally connected to it and check where that goes. It's probably a loose contact somewhere. But the easiest thing to do would be to solder a wire with one of those crimp contacts that you can mount under a screw, and then attach that to a screw behind the dash going straight into a solid piece of chassis. (around the fuseboxes for example, or just use one of the grounds there.)