Wiring 434mhz transmitter to Explorer Hat
Connect pin one of the RF chip to ground.
Connect pin three of the RF chip to +5v.
Connect pin two to both one of the outputs on the HAT and to +5v (via a resistor for the +5v).

The connection to the HAT output should come between the +5v and pin two of the RF chip, so when the switch is ON, the signal goes to to ground and not to the RF chip's input.

Note that this setup has the effect of reversing the switch behavior so that when the switch is OFF, the RF chip will transmit ON.