I have a 1970 GTO conv. with a 400 MT and am trying to determine if the temp gage is screwed or the sender is. Ran into something here and I have the usual sender but also a water temp switch and they are linked by wire. I have 11.75 v at the sender and when I ground it the gage needle just flutters slightly, otherwise no movement so I assume the gage is done. The question is What is the water temp switch for if I have a sender? Nothing in the manuals or resto books. Any constructive feedback please??