Finally, a friend at a good shop printed out a comprehensive diagram for the OD circuitry from a website service that he subscribes to .  Lo and behold, there is a +12volt side to it, wouldn't ya know.  (What else would the ground be there for?)  Lo and behold, the +12V runs through a brake pedal-acctuated switch, which I had mounted with the dash harness, but did not understand.  (I thought it was cruise cancel.)  It is the lower of the two brake pedal mounted switches, and it is OD cancel, not cruise cancel.  Well, it might cancel cruise, too, for all I know.  I removed all my cruise gear, so it doesn't matter. 

 

Anyway, I had not properly adjusted the switch.  It was too far away from the pedal, so it was as if I was constantly pushing in the brake pedal away from the switch, which is how it disengages the OD, by opening the +12V side of the OD solenoid circuit.  Once I pushed it in all the way against the pedal, it began to work instantly.  (The rest of the circuit, the return side, is sunk through the computer when it decides that you have reached at least 45 mph.  Thus, with no brake, but no 45mph, you have +12V, but no ground, so no OD.  No brake, 45mph, ground is made through the computer, OD hooks up as soon as you let up on the gas or reach 54mph.  OD will hold all the way down to 37 mph on mine, but once I touch the brake pedal, +12V drops, and the solenoid pulls back, dropping the OD.  Once below 37mph, the computer opens the ground circuit, and OD drops out.)

 

Live and learn.

 

Steve