A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a 12 volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it's not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.
In this case when the short is removed, the test light will still be pretty bright because it has much higher resistance than the head light bulb. If you have another head light bulb, use that with the jumper wires. When you do something that removes the short, both bulbs will get half of the 12 volts so they'll both be half brightness.
This is all assuming you have normal light bulbs, not those dangerous and obnoxious HID bulbs. If you have those, suspect the ballast is shorted. The price has come down on those bulbs and ballasts but when they first came out, each of them cost around $800.00.
Friday, October 26th, 2012 AT 4:45 AM