temp gauge problem

[supturb89]

Short story long
96 205 with the 350 TBI

My temp gauge since purchasing the boat is always pegged. With the key off it always pegs to the right. When you turn the key to the ON position the needle moves ever so slightly more to the right. When running the boat it never moves from this position. The PO told me the gauge didn't work and that it was the sending unit. I have replaced the sending unit and the problem still persists. Rmoving the wire from the sending unit causes no change, which leads me to believe it could be a ground issue? I am electrically stupid so that also adds to the problem. All connections on the back of the gauge seem to be tight. I have checked the connection for the wiring harness behind the gauges and it seems to be nice and tight with no corrosion. Is it possible the gauge could be wired incorrectly? On the back there are two purple wires wired together on a post. A tan wire by itself on a post and the black ground. There is also a blue wire which I assume is for the gauge illumination? What should be my next steps, keeping in mind that you will have to explain it like I'm three years old if it has anything to do with an multimeter, which I do have. Another issue that makes this more difficult is the fact that the main wiring harness coming in behind the gauges is so short that I am unable to pull the gauges out far enough to see or work on anything behind the temp gauge.