Short in Rear Lighting Circuit

Am having a very difficult time locating a short circuit in the rear lighting circuit of my 1998 TM2619. I've narrowed the problem down to the section of the circuit past the connector that hangs under the floor near the refridgerator. I've been over the wire on the outside of the trailer, removed the interior ceiling moulding, and pulled out each effected light fixture - but haven't found anything that would cause a short.

Was wondering if anyone had some experience with how to trouble shoot this type of problem and locate where the short is occurring in the circuit. Any help would be appreciated.