Blown fuses are caused by a direct short (As opposed to an open short, where no circuit can be completed). If you remove the bulb from the circuit and the fuse still blows, you may have found your problem. There are, however; other loads on the same fuse, and sometimes people install their accessories on marginally fused circuits, causing any additional load to cause the fuse to fail. Overhead lights normally light when a ground contact is made such as the door switch, or the direct ground in the switch. Assuming a switch/socket assembly, the switch can be checked with an ohm meter: with no bulb in place and both wires disconnected, resistance between terminals should be infinity with the switch in either of the two on or single off positions. With a bulb in place and the switch in one of the on positions, resistance should be a few ohms due to the filament being a resistance circuit.