The way the OD circuit works is, there is a wire that goes from the hot terminal on the coil to the coil in the relay. It then goes out from the other side of the relay coil, down through the kickdown switch, then the reverse lockout switch, then to a governor switch which is grounded on one side. The reverse lockout switch prevents the relay from energizing when the car is in reverse, if the car is not in reverse, the the circuit is from ground, up through the governor switch so when the car reaches 29 mph, the governor switch closes (due to centrifigal force) and then the current flows through the lockout switch, through the normally closed contacts on the kick-down switch, through the relay coil to the hot terminal on the coil. This energizes the relay which pulls in the contacts and sends current from the hot battery cable (which is connected to the starter solenoid) through the fuse, through the relay contacts and to the solenoid. The solenoid energizes and when you let your foot off the gas, it slips in and holds the sun gear stationary so the car can operate in OD. A good test is to make sure the car is not in reverse, the OD cable is in, and the ignition switch on, jumper the terminal on the governor switch to ground and see if you hear a loud snap from the solenoid energizing. The relay makes a soft click but the solenoid makes a loud snap and that's what you should hear. If you do, the "low circuit" is working. If not, it's either the relay, the governor switch, the kickdown switch (look for corroded contacts on it) or the associated wires. Otherwise, check the circuit from the battery, through the fuse, contacts to the solenoid. It is probably wise to remove and check the solenoid first.
Tarnished contacts inside the solenoid can cause the problem - there are two sets of coils in the solenoid, it requires both to pull the solenoid in and when it does, there's a set of contacts that breaks and takes one set out of the circuit to relieve the load on the generator / battery since only one coil is necessary to hold it in after it fires. If those contacts are tarnished, it will not throw in.
Kaiser Bill has a good solenoid test on this site at -
http://www.kaiserbill.com/Web-PDF/OD-Solenoid.pdfIf you do bench test the solenoid be sure to use a good, fully charged battery to do so as a battery charger cannot supply the current necessary to energize the solenoid.
To test the relay, you can touch a 9 volt radio batter to the two terminals (I believe its the rear terminal and one of the side terminals, polarity doesn't matter) and see if it clicks.
Also, do you have the circuit diagram? If not, I can scan it and post it here because it is very helpful.
Let me know.
