1993 Ford Aerostar coolant temp guage swings

There is a slosh module in the back of the instrument cluster that controls guage movement and that may be failing on the temp sender side, usually when completly bad guage needle will swing to either extream of the scale. I once had an arostar temp guage issue that was resolved after adding a ground wire at the temp sender to a ggod ground off of the engine, aparently the intake manifold was loosing electrical continuity with the engine block. I had a few other Fords that the base problem had to do with poor electrical grounding of engine. Like I'm sure at this point you or someone has had to service the battery terminals, and if not start with the negative one, The terminal end will look normal but they corrode from inside the wire out.