First, make sure that when the OD switch is off, the solenoid on the OD is NOT getting power. I beleive the 69 had a power relay in the circuit. Switch turned the relay on-off, the relay powered the solenoid. 4th gear switch would also have to be stuck on for this to happen.

Test: Drive auto until symptoms appear. Find a safe place to do the following test.

Ignition on, Engine off, 4th gear, switch on OD, get under auto, remove wire from solenoid which should click off. When wire reattached, should click on.

Switch OD off, check under auto again. If solenoid reacts to wire being removed and added back, relay or something is circuit is still allowing power to get to solenoid. See below.

If during the first part of the test, the solenoid does not sound with a sharp metalic click but a dull thunk or no sound and wer is at the solenoid, your solenoid needs to be refurbished. I'll have to send you instructions.

Be aware that the relay may drop out if you turn the ignition off. You may have to test for the presence of Off power with the engine running.

Duane