Part 4 isn't a premade controller unlike other components. Instead you have to make it. Its not that difficult, There is no real realistic way to describe how to make a part 4 controller, so instead I have made a example one to help convey my idea into a visual explanation:

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2866344732

To make a part 4 controller you require the following conditions:
-Have a composite output on your controller
-Have a master switch input on your controller
-Have a composite switch box inside and hooked up to the master and comp output

Please do not use channel 31 or 32.

Make sure on your controllers that processes the External Unit Data receives the information on the same channels you used in the Part 4 controller