I installed Mid50's 12V temp gauge in my 54 when I restored the gauge cluster and Mid50s said that mid scale on the gauge was going to be 160 degrees, which meant it would peg the gauge at around 190-200. Since I like to run my motor temps between 190 and 200 to burn off any condensation, I knew I would have to adjust the gauge. A friend has a device that allows you to dial in a desired temp and plug in the sender. Once the sender is hooked up to the gauge and 12V is applied, the gauge will indicate a given temp. You can do this with water heating on a stove but this was much less messy for me. I set the temp at 190, hooked up a decade board between the sender and the gauge, and found that 50 ohms of resistance will produce a mid scale reading at 190 degrees. I also found, using the 50 ohms, that it required 145 degrees to move the needle off the peg to the very first mark - 170 to the 2nd mark (1/4 scale) - 190 to midscale - and 213 to the 3/4 mark. I'm using a 180 thermostat so I will set my electric fan to come on between mid scale and 3/4 scale, about 195-200 degrees. Keep in mind that no 2 senders are the same but they should be close.
Ken

 

That's great information Ken! So what you are saying here is if you want to calibrate this gauge for mid scale 190 degrees you just add a 50 Ohm resistor in series with the sender to the gauge? Granted their will be some minor readings differences between gauges, senders, resistors. I was wanting to buy the Mid 50 temp gauge but knew I would have to calibrate it. You just did the hard part for me! Now I just have to get down to the local Radio Shack and see if I can buy a 50 Ohm resistor or a combination of them to make 50 ohms before they close the stores for good......

 

Yep, 50 ohms in series will do it. I used a 1/2 watt resister because that's what I had but this is overkill - not much current flowing here. It would be nicer if the gauge had numbers instead if marks but that wouldn't match the other gauges.
Ken