Trying to find a 12-volt short circuit can be a frustrating and tedious job. However, if you remember one simple rule of thumb, the job gets much easier: All circuits require continuity (an unbroken path of electrical current). If you have a 12-volt short circuit then somewhere, that path has been broken. Follow these simple steps to find out where the break is.
Set your multimeter on Ohm. This will read not the voltage, but the continuity of the wires you will be testing.
Pull the feed wire from the component that is not working and attach it to one of the probes of the multimeter. The feed wire is the wire that comes from your 12-volt power source to the component. It does not matter which probe you use as long as you are attached to the feed wire.
Pierce the wire 12 inches from the end attached to the multimeter with the remaining probe. If you register an Ohm reading (it does not matter what the reading is), the short circuit does not exist between where you pierced the wire and where the wire ends at the component.
Pierce the wire again, 12 inches from where you just tested it, away from the end of the wire. Continue testing the wire until you find the point where no continuity is read by the multimeter. Replace that section of the wire and test again to make sure continuity is restored.
If you are working on a component that is far away from your 12 volt power source, use some 14 gauge wire to extend the length of the multimeter's probes by attaching the probe to one end with a double ended alligator clip and use another at the opposite end to connect to the wire you pulled from the component.
Make sure that the wire that you pulled form the component and attached to the multimeter can not "ground out" by touching any metal or exposed wire. This will give you a false Ohm reading.