Ford Repair: relay that controls dome light, door latch, relay switch

Question
vehicle is a 97 ford ranger. problem is the dome light will not go off until i notice it (when it is dark outside) and this could be 2 or 3 hours later. It seems that the problem only happens if the drivers side door is opened.
Opening the passenger side door does not make it stay on.
Neither door is ajar.
Someone said it is a relay switch inside the door...is this true?, and can I buy this switch over the internet or is it available only at dealer?

Answer
There is a switch in the door latch, however this will usually also cause door ajar light to stay on. The problem could be several things, including the GEM nodule. On some of the first Rangers with GEM modules there were various symptoms related to that system.

Most likely the door ajar switch is sticking, this is very common on Fords.