Okay, this is gonna be a real short tutorial. I'm not gonna go into depth in anything and I'll just give you the general idea. Mue originally attempted this, and while all the code made sense, the script didn't fire when the lever was hit, even though it should've.
So, to start, you're gonna place the lever with the ID 9E, as it is in the overworld with area ID 13. Next, create a type 8 interaction with the ID 501 (It might work with 500, 502, 503, 504, etc...) and place it where the lever is. Then, create a script to fire in the room. You're gonna perform a tile check, and although you would THINK you're checking for the tile 9F, you're not - you're checking for 00.
For some reason, the game replaced the trigger with tile 00 instead of the contrasting lever id. Why, I'm not sure, but here's an example script.
writelocation FEBE
setinteraction72 2
checktile 33 00 //Check to see if the lever at 33 has been changed (00)
//Action
Not sure for the reason behind these events, but hey, it works fine, so who cares!
~Lin