I am replacing the thermostat on a Kenmore electric dryer.
I need to know which terminal the red wire goes on.
There are 3 terminals numbered 1, 2 and 3.

The correct way is to change one wire at a time if the thermostat is the same as the old one. If you pulled all the wires off the old one without marking the wires, the only way is to look at the wiring diagram which may be located in the headboard.