When replacing a cable or loose wire that is threaded through a maze of clutter and bulkheads, it is easier to attach a "pull cable" to the old wire before removing it. The "pull cable" will allow you to pull your new wire or cable back through the same route taken by the original cable. Another advantage to using a "pull cable" is that the replacement cable will be of a similar length to the original, and electrical shorts and fires may be avoided. You may even avoid skinned knuckles.

The "Pull" Cable...

Tie or tape a suitably flexible piece of string, cord, or wire, to the cable to be replaced. Ideally this should be about two feet longer than the part replaced. Pull out the old cable and allow the "pull cable" to follow until a few inches of the "pull cable" is past the final obstruction or mounting point. Next, remove the old part from the "pull cable", and tie or tape the new cable to the protruding end of the "pull cable" so that it is secure. Slowly pull the "pull cable" back until the new cable is in place, avoiding any kinks and working past any snags along the route. When done, make off all connections and move the cable as necessary to even out the slack at each end to remove any undue stress.

An Alternative...

If you are running a new wire, you may not have the luxury of being able to prepare a "pull cable". If you are lucky enough, you may be able to get your hands in the confined space to pull the cable through. More often than not this won't be possible. The solution is to use a stiff length of wire as a "pull through" or "fish tape". Push this through where you want to run the new cable, and then use it as a standard "pull cable".