[IMG]http://www.mastertechtrans.com/post/kd2.jpg


You have correctly identified the problem; the black wire which feeds the kick down solenoid is also the ground for that system, the solenoid body is an electromechanical relay, in contact with the solenoid valve, grounded thru the transmission case.

Sam,
Here is what I mean by the above statement.

Yes you are right; the single wire going to the KD solenoid, supplies the necessary operating voltage, once that VOLTAGE is consumed by the load place on it, the solenoid coil in the body moving the solenoid valve piddle, Electromechanical Relay, it continues to flow thru that circuit, becoming the circuit ground side, transmission case back to the battery completing the closed loop. As Illustrated below.

Picture #1 is a voltage reading In a car, using the KD switch power supply wire, and feed wire which goes too the KD solenoid on the transmission as the ground source.




Picture 2, channel 2 is the voltage into the KD solenoid, 13.86 volts is power flow to the solenoid

Channel 1 is the KD solenoid ground side. 0.12v is the voltage dropped by the load, ground side.

I hope this helps.