Does it blow fuse when disconnected from bulb?
If it still blows fuse, then there's a short. Either the wires have rubbed off insulation and are touching. Or the plug terminals got hot enough to melt the plug and are shorting there. Carefully inspect the ends of the plug, the terminals and all wiring going to it.
If nothing obvious, connect voltmeter to plug terminals with everything off. should have infinite resistance between the plug terminals. otherwise there's a short.