What kind of OD? I believe Spits used either D-type or J-type.
One problem I've had on a J-type is the quick connect being just a tiny bit loose on the solenoid tab. Not enough to pull off with a tug, but enough to wiggle. Sometimes it would make contact, and sometimes it wouldn't. Crimping the wire terminal tighter solved the problem.
For a D-type, there will be a relay, and I've also had problems with the relay going intermittent. Adding a diode across the contacts seemed to help a great deal.
Also, troubleshooting an overdrive without a pressure gauge is just shooting in the dark IMO. Get a pressure gauge and use it, it will quickly lead you to the problem. There's a fellow that sells them on eBay from time to time for about $50 (including the adapter for your model of OD). I think his name is Jay (or James) Holecamp, but I don't have contact info handy.