Turn your key to "on" and start checking out all your electrical devices--sunroofs, lights, gauges, etc. Check for errant behavior. Finding shorts is kind of a dark art without grabbing your multimeter and checking everything. If you can locate the circuit the short is in, there are wire testers that can tell you approximately how far down the wire the short is. You will need some wiring diagrams and a little ingenuity, but you can do it.