and sorry if i miss lead you, or others here. when the car was running at 190, he set the blue-line to that temp, to match the mechanical gauge, that was in the top of the radiator.,,,,,,,sorry `bout that chief!
OK, he MUST have a sending unit of some sort. He had to. There is no way in heII it could have worked without one. No way. He simply never had the *correct* one for it. Now if you knew what sending unit he was using and what resistance the rheostat was set at, then you could duplicate how it worked. Just get a resistor close to that value and either put it in series with the sending unit wire or parallel from the wire to ground. That could be done at the gauge end. If you know what kind of vehicle it was in ask him if that is what sending unit he added the resistor to.... if it had it's stock sending unit.
yes, tony, correct. he put it in-line between the sender and the gauge. when the engine was running at 190, "with the mech. gauge sender in the top of the radiator", he set it to190, on his blue-line, to match the mechanical gauge.