BMW: No Electricity to Back-up Lights, fuse box, drive shaft

Question
I am working on my '85 325e (E30) because the back-up lights don't work.  TESTING: I put the car in reverse (manual transmission) and turn the key to the run/on position.  After no lights came on I removed the tail light housing and used my multi-meter to check for power at the plug the tail light housing plugs into when installed.  Incidentally, the other lights (tail, brake, and signal) all work.  

I have replaced the fuse in the fuse box and the back-up switch.  I even tried bypassing the back-up switch but still no reading on the meter.  I do not know where to start looking for a disrupted power supply.  

Answer
RSANCHEZ,

 Check the wiring that runs from the Transmission up through the tunnel beside the shifter boot.  Sometimes the wires fall off the switch, or break.   There is a switch on the side of the tranny that controls the back up lights, if this switch is bad then they will not work.  Make sure the wiring has not come in contact with the drive shaft as well.  The rubber coating on the wires will wear off and ground out on the drive shaft.

 Let me know if I can help any more.
 Josh