Help... Adding a second temp gauge

I think using 1 sender for 2 guages is only going to be a bad result.

The sender (typical aftermarket) uses a variable resister to cause the guage to move, adding a second guages to the system changes the resistance of the system.

The factory sender does the same thing but the supply voltage to the guages is not a continuous voltage it is a square wave, 12v on then off then on then off etc, the average voltage is in the 5 to 6 volt range. That is probably what you are seeing with your new guages fluctuating