Let's call one side of the switch the "Right Side" and the other the "Left Side.
* Right side upper post goes to Light
* Right side lower post goes to Heater
* Right side center goes to "110 volts".
* Right side upper post, where Light wire connects is jumpered to "Left Side Lower post.
* Left Side Center is connected with 'Right side center then is wired to "110 volts".
* When switch is up, only light lights.
* When switch is down, the heater is on AND
the lower left post supplies 110 to the upper right post via the jumper between the upper right post and the lower left post.
Adios... Jasper.