I need a double-jointed height-challenged person with extensible eyes! 

Rickles:

 

     >The under-floor cable is definitely faulty and I will have to replace it. However, access to one end is going to be a nightmare. The person who initially installed it must have been a contortionist<

 

Do you have access to a skinny teenager?   Another trick if straight run, securely bind the new cable to end of old one and see if it will pull through.

 

Using the old cable to pull a new. Best option. Unless someone looped it around a nail.

Well, we've been told that it's stapled in place...