Here's a simple schematic of the overdrive system for the 2wd vans:
As you can see from the schematic the OD circuit becomes live whenever the ignition is on. The thermo switch and the OD switch are there to disable it. The relay contacts (between terminals 1 & 2) are normally closed (constantly supplying power to the solenoid). When ground is applied to either pin 3 or pin 4 (via the switches) the contacts will open, removing power from the solenoid. When you have power to the OD solenoid the OD should work. If the solenoid has power but the OD doesn't work, then the solenoid is bad.
If there is power to pin 2 but not pin 1 then the relay is preventing OD operation. If this is the case, then check for ground at pins 3 & 4. If no ground is present at either of these pins but no continuity between pins 1 & 2, then the relay is shot. Make sense?
For more information on troubleshooting go to the electronic service manual start testing components. The OD section starts on page AT-14 (PDF page #310). If you don't already have it, here's a link to download:
https://drive.google.com/file/d/1q4u...7wOD7nKyF/view