The 1991 and later Hatch (the ones with the Megamos factory alarm box underneath the passenger seat) have a switch integrated in the lower part of the lock. A red/wite and a brown wire are connected when the upper latch is inserted all the way down. The wires lead to a smapp 2-prone connector that resides under the foam like cover, very close to the ground strip.
When the wire breaks off, of the connector dislodges, the hatch light will go on when the doors open but everything remains dark when you open the hatch.