I just came from the garage. I fixed the relay switch assembly myself. I will now describe my symptoms, diagnosis and repair for all to benefit from.
SYMPTOM--- wipers would come on sometimes, not always. In the end, they come on, but when I turned off the switch on the dash, they stopped dead, and did not park. Couldn't start them again with dash switch. I have the GM hideaway wipers (2 speed depressed park).
DIAGNOSIS--- I tested the wires going to the wipers and the grounds. They all appeared fine. Here are the tests. The case of the wiper motor and gearbox are always grounded. Test with test light for ground. Check black wire that connects on a separate tang to the wiper cover. It should be ground also. Pull off the 2 wires on the washer pump, which is basically the cover of the wiper gearbox. The yellow wire is 12 volt power when key is on or in accesory. The dark blue wire is ground when you push the washer button on the dash switch. In any event, the washer system runs independent of wipers, so pull off both wires, and tape ends off to avoid sparks while testing the rest. Pull off connector with 3 wires just above wiper motor. Middle one is yellow, must test as power with the key on or in accessory. The light blue wire must test as ground, when the dash switch is in low wiper speed. The third tang is green on mine, and will test as ground also, in wiper high. (I think it also passes ground with key off, but I would have to check my wiper diagram further on this point). There is a red wire going to wiper gearbox also. It must test as hot, ie. 12v power at all times, even with key off. This is what will get wipers to run after the key is off, so they will park.
In my case all wires checked out okay. So I pulled wiper motor out of car, put on bench.
With washer cover off, you will see a green plastic switch on the bottom of the gearbox. Remove the one screw holding it in place. Lift it out a bit. You have one red wire going to one side, and a black with pink stripe to other side, (this latter wire goes into the motor). This must pass power from red to black\pink, when the switch is out of place, as the park position has been avoided.
In my case, I had no power passing thru the switch. Also, test the relay part of the switch. Put power to the middle tang on terminal board, the yellow wire spot, and put ground to the light blue wire tang, closet to bottom of wiper. The relay solenoid must activate to pull the metal part of the switch against it (creates magnetic force).
The REMEDY--- I had no power crossing the switch with it out in my hand. SO I took off the black plastic cover on the back of switch, with tiny screwdriver. It will come off to reveal a set of points. I cleaned the contacts with fine sand paper. Had some black carbon on them. Put cover back on. Tested with voltmeter. I now passed current from red to black\pink wire.
Put switch back in place.
The ultimate bench test----- put power from battery to red wire. ground the case to the battery. put power to yellow wire spot, being the centre tang on terminal board. Put ground to the light blue tang, being one closest to bottom. Voila, wipers fire up and run until ground it taken off the tang on terminal board. Then the wiper motor will continue to run for a couple seconds and park
ADDITIONAL SYMPTOM--Running in and out of park--- If your wiper motor seems to run into park, stop for fraction of a second, then run again, then stop and run, up and down into and out of park, the relay switch must be "adjusted". Big thanks here to Corvette Specialities of Maryland. HE told me how to adjust. Basically put more drag on the armature, by tightening set screw at end of armature, being top of wiper gear box. You will see set screw and lock nut. Putting some tension on the armature will prevent the wiper momentum from forcing wipers out of park position and back into the run position again.
Sorry for long post, but all is fresh in my mind, so I thought I'd share it with you.