I would say two things..

first.. it's not a short, it's an intermittent open.
second.. if you locate the approximate area of the open, then use an exacto blade or a razor blade to open up the outsite sheathing.. pull off about 2- 3 inches if not too close to the adaptor or plug end, then plug it in and wiggle the indvidual wires until you know which one it is.. then cut, strip, twist the wires and solder it.. then tape it all back up. If it's real close to the adapter end, you still might be able to open up the box with a dremel tool, cut a few inches of the wires off and resolder them inside the box. then use my favorite epoxy "JB weld" (found at any automotive store) to glue it back together. simple job, should only take about a half hour or so.