Attic Thermostat

I need some help installing an attic thermostat. The thermostat has 4 wires inside 1 white, 3 black. 2 blacks are attached to the internal workings of the thermostat and the 3rd is used for power. I know the 3rd black along with the white is used to connect to the power supply. I believe that the other 2 blacks can be used for an on off switch. If I don't want an on off switch, I just cap off the 2 black wires, correct?
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