the leather belts that connect h
靷 refers to the leather straps or belts used to connect a horse to a carriage or cart, specifically the traces that pull the vehicle.
靷 combines 革 (leather) with 引 (pull), suggesting a leather item used for pulling. This is a straightforward semantic compound.
The left side 革 means leather, and the right side 引 means pull. Picture leather straps pulling a cart: those are the traces.
For イン, imagine the leather straps are inside the cart's innards: inn -> イン, and the straps pull from within.