Here's a photo of the right side of the engine on my YM1110D. Just behind the air cleaner you can see the reservoir with a small fuel line going down to the TS plug. The plug is threaded into the intake manifold, and has a wire connected to it with a small screw.
The TS is NOT supposed to be on with the ignition switch in the run or start position. If it is, then you will continuously drip and burn fuel in the intake manifold all the time the tractor is running. The reservoir will empty, and you will probably burn up the TS heater.
Turning the switch to the left is supposed to turn on the TS, but I think the better way to set this thing up is to have a separate momentary contact switch to run the TS like the 1500 was described above. That way, you could also run the TS while cranking the engine rather than just putting it on before cranking.