[hypoxia]

"SOLVED" I think!  Tracing the DEF Line Heater wiring a single orange wire runs from the Rear Load Center and is spliced to all 3 DEF Line Heaters EXACTLY centered over a frame rail above the tag steering accumulator.  I could barely touch it and ran my bore scope in there to see how it was assembled.  I decided to cut the splice out & look what I found.  The splice was the 3 DEF Heater wires twisted together with the power wire laid on them and a drop of solder to make the connection.  Cold solder joint on 3 the strands of the power wire, the remaining strands were not attached in any way, and NO mechanical connection.  It was all held together with shrink tubing.