Soldering the relay may solve your problem. I made up a test harness to check the circuit, just for grins. It went like this.

Items needed:
lighter plug for lighter in car, blade fuse holder and fuse, on off toggle switch.
All available from your local car parts place. I forget the fuse value , but use the one for what ever fuse the relay uses. Do put in a fuse!!!!

Install:
The wire from the relay comes down the gearshift hole under the car and has a connector just below the shift linkage. My connector was a round one a "bullet" connector. snake the wire down and connect it to the single solenoid wire.

Testing: Drive around and flip the switch. The OD either works or not. If not then you could be dealing with a intermittant solenoid or maybe even a valve body problem, but that's a whole different story.

Hopefully the resolder will fix it, but if not try the wire! Be sure you hear the solenoid Click every time you shift the switch! Dont start the car, but turn the key on, actuate the switch while listening under the car. Might want two people for this! The click of the solenoid is fairly audable under these conditions

Good Luck!

Woody