Bill,
UberRoo posted the below pic in a different thread talking about cutting the Solenoid C wire. He mentioned the following instructions:
"Under the dash is the TCU. If you look at the picture, there are three plugs going into the TCU. The upper plug (highlighted in red) is the one that goes to the transmission. The green wire with a red stripe controls solenoid C. All you need to do is cut that wire and splice in a switch, which will normally be left ON, but turned OFF to engage the rear wheels manually."
Full thread can be viewed here:
50/50 Torque Split thread
-Chike