locking problem

I have a locking problem with my 2000 galant. When the ignition is on, the doors lock fine, no problem. when i take the key out of the car, open the door, and press the lock from the panel on the door, it won't lock. Is this a blown circuit? The overhead light is not in the car and i bought it like this, so is this maybe a problem related to that? It worked before installing a new head unit, so maybe something was reset? Anyone have any suggestions or should i take it to the dealer?

Take the head unit out again, see what happens.