I have read all the past posts about coolant temp guages and sending units. What is the definitive test to tell if a stock 1969 console mounted coolant temp. guage is broken (vs. the sending unit)???? Mine worked last year just fine , now it doesn't vary with temperature. Grounding the sender "post" on back of guage "pegs" needle hot. Guage dos not go to cold when sender is disconnected. Going from boiling water to ice water shows little change, almost none ( how fast should it react ? ). I was going to put a variable resistor across it next to see if I can get it reponding. Thank you in advance for the help !!!