farmall -
There should be two light gage wires leading into the right side of the O/D unit at the back of the transmission. These are NOT the same ones that go into the transmission itself. One will be hot and the other ground. The one with the stripe should be ground. I can't say for sure since I never saw the donor truck. Splicing directly into the hot wire will allow you to manually control the unit. Power on = OD on, off = 1:1. Because it acts seperatly from the rest of the transmission, it will remain on through all three gears if left hot. Makes it a bit sluggish from a stop. However, I usually don't have a problem with it and only turn it on at cruising speed.
I really like the control it gives me. Cruise speed is now at a decent rpm and it can even function as a gear splitter of sorts.
Isaac.