You can use this code if you have custom ability, but based on original 'searing arrows' . That's ok, because order id cannot be changed and is still 852174 / 852175 for right click-activate and deactivate ability.
Make sure you didnt write anything to Custom Value of units. It is reserved for Unit Indexers. Import Bribe unit indexer, if you dont have any indexer already in your map.
You can use , waht I send this way:
create trigger named ord, convert to custom text. Delete all inside this trigger, copy/paste code from previous post.
Its basicaly setting boolean flag for any unit that activate/deactivate your ability. Tocheck if unit has activated ability use this boolean
isSearingArrowActive[GetUnitUserData(YourUnitHere)]
it returns true is ability is activated, false if it's deactivated.