I *think* that's the wire that powers your gauges and radio, possibly the ACC slot on your key or something. I'll have to check my book at home to be sure though. Perhaps pull your dash and make sure your radio harness isn't rubbed through.
That is a nasty short though, no doubt.
On my truck it goes to a suspiciously thick, pink and black wire before going into the cab bulkhead. It's one of the few fusible links that are still intact on my truck, so I've got no offhand knowledge on it.