Since you're not connecting a light, just connect the Pink and Yellow wires to the center and one of the outer posts. See my Post # 13. Here's the starter switch page from my 2015-17 Slingshot Service manual -
Knowing that shorting the Pink and Yellow wires in the connector that normally plugs into the connector to the starter button starts the engine, I assume the OEM switch uses the Pink wire to supply power to the switch where the power is split to power the light with the ground wire completing the circuit for the light and the switch itself connects the incoming power to the Yellow wire that triggers the starter motor.
To test for yourself, just turn the ignition key to the Run position and then short the Pink and Yellow wires in the dash and the engine should start.
THANK YOU!!!!!!!!!!!!!!!!!!!!