New Uline Thermostat Control UL2783. Has number 1,2,3 beside connectors.
Wires are red, yellow, white/blue. Where do they go?

We cannot tell because I have no idea what kind of ice maker you are fixing and the whole story. Why are you replacing it? Did you get a diagram with that thermostat? You should have received one with it. My guess is that one wire is common and one is normally closed and one is normally open. You may use only two: the common and normally open. That's how Whirlpool ice makers work.