Welcome to the forum!

To throw the switch in your track plan, you can use the 153IR accessory at the bottom of your wye.
https://www.lionelsupport.com/media/servicedocuments/71-4111-250.pdf

When the train passes it, the switch will throw to the opposite direction.

Here is a video of the controller hooked up to an accessory.


A short introduction to the 153IR is here.
https://lionelllc.wordpress.com/projects-and-tips/wiring-your-layout/introduction-to-lionel-accessories/lionel-accessory-activation-153ir/

Owning and operating Lionel trains will teach you to become 'electro-savy'.


Larry