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.
For intermittent problems like yours the bulb may be dim already. Watch what takes place when it gets bright. That's when the short is occurring. One valuable observation is to see if that short occurs any time or only when you press a switch, and which switch. That will give you an idea of where in the circuit the short is. If those switches are on the door panel, suspect broken and frayed wires between the door hinges. You'll be able to make the short change by opening and closing the door.
Also be aware a brake light bulb limits current to about one amp. That's not enough to run a power seat motor, so the motor is going to run very slowly, if at all, AND that test bulb might get pretty bright even when the short is not occurring. A better alternative is to use a head light bulb. Those will allow at least five amps to flow. The motor will run better, but that bulb will still get full brightness when the short occurs, and it will still limit current to a safe value.
Thursday, January 9th, 2014 AT 5:21 PM