[SS Tim]

The PO probably pulled the electrical sender to install the mechanical line. Look around the the engine, whatever you have, and see if there is a 20ga dark green wire with a plastic connector. If you find the wire pull loose the cluster connector and resistance (ohm) check the wire. If it is good it will be very very low. Then and with a good cluster I'd worry about installing a new or known good temp sender. The factory manuals are a great help in sorting these things out. Get both the MY specific chassis and the overhaul manuals. Haynes and Chiltons are usually to generic to be helpful.