Skunk---
When I first encountered the "mysterious" J-type OD, I got on the board and asked some questions. Duane (OD GURU) was gracious enough to lend advice and sold me some parts. This guy knows the OD units and if you are patient and are willing to go through the troubleshooting process methodically, Duane can lead you down the enlightened path to Overdrive Bliss.

It's been said before, and it's true, that among the many people on this board, almost every problem has been encountered and resolved.

I know we all have opinions, just as we all have assholes, but we are here to help solve problems, not blither about who knows or does not know things. I think this thread could have been a little bit shorter had we just collectively agreed upon a good plan of attack to pinpoint the problem.

I have found that the OD relay is stop #1, the solenoid stop #2. With the wiring diagram in this thread, it is a very straight-forward process to determine if the relay is bad. Some wire, a few alligator clips, and if you really want, a multi-meter. The same applies to the solenoid---You just need 12V to the hot spade on the back of the solenoid, making sure your ground wire is in good shape and has full continuity. (now that's 75% of the problems right there in two simple steps)
Once I know the relay is ok, next step is to probe the wires to/from the relay for proper voltage. Again, the diagram in the thread is more than adequate.
Hopefully the problem will be on either side of the relay and be straight forward....ie--bad wire, bad 4th gear selector switch....
A previous thread mentioned a "redneck" solution to jumping the od relay and selector switch, and directly powering the solenoid. That's a very good option as well. I've done that with the car in the driveway with the rear up on blocks. Plop it into 4th and jump the od....it works or it doesn't.

Still, what it comes down to is methodical troubleshooting, using a checklist if you wish. Test each component in isolation, determine functionality, move to next component. Test continuity between components, eliminating any if needed.

The wires coming/going from the shifter knob switch get gnarly, esp. with the crap insulation and constant movement of the wires from shifting gears. The relays sometimes suffer from weak cold solder points and get intermittent....you can pop off the top plastic cover and see the condition of the internals if you wish. I've found it never hurts to remove the solenoid and inspect the two o-rings on the shaft and clean the old thing with electrical cleaner, dry off and coat with new ATF or 30wt oil.

In the worst case scenarios, you will be pulling the OD unit off the back of the tranny and replacing the o-rings on the pistons as the 2-pc PTFE seals blow by--OD GURU can source you the parts--and you will be checking the filter screen and relief valve innards, and the piston pump assembly.....all replaceable parts if need be. ---I ended up having to replace the high pressure, inner relief-valve spring in my '86 OD as the spring actually broke in half.........totally throwing off the internal pressure.

This is not a job that's going to get done quickly, it's that simple, and you may have that unit in and out a few times....I have on a few occasions, but patience, a reasonably warm place to work...even maybe a lift, will make life so much better.

Electricals are frustrating, but just think of circuits as pipes with water flowing through them....it helps me.....and think of the whole job as a great learning experience, because if you don't learn anything from it, you'll be repeating it again, and again, to much frustration.