'92 240 Wagon: Need to replace rear passenger speaker wire

[craigsan42]

Just replaced the factory radio in my 240 wagon. The new stereo played nice for only a week before shutting off the volume each time I turned it on. Checked all the wiring for the adapter harness that I installed. All connections seemed fine. Then, disconnected the rear passenger side speaker. Now everything works fine with that one speaker disconnected (!!!same speaker was crackly prior to stereo installation). Thus, I've deduced that the wire is bad that runs to that speaker. Perhaps it was clipped between the door and the frame -- although the rubber corrugated jacket between the door and frame is in place and functions fine. Or, maybe I have a poor connection at the amp. Does anyone know how the connection to the amp is made, and how I can figure out which one is the rear passenger speaker wire? If I need to run a new wire from the rear passenger door to the amp behind the dash. Has anyone done this?