1995 Ford Ranger • 341,000 miles

Replaced door Ajar switch, (which was a pain), on driver's door. It appears that there is only one way to install and one way to plug harness, but now the dome light comes on when you shut the door and off when you open it. There is no way the harness could be plugged in backwards so what could be the problem?
October 30, 2013.

If you are sure the wiring is correct, then you must have gotten a bad switch. The switch is a simple circuit. Either it is an open or closed circuit. Reversing the wiring shouldn't cause this problem. I think the switch was put together incorrectly allowing the circuit to close when it should be open and opposite.

I would recommend trying a new switch.