I've been working with the service manual and also searched this site, including going through the stickied Windshield Wiper System manual provided, but I am stumped, thus I am asking here.

The vehicle is a 1990 Custom Cruiser with the round motor modified pulse wiper system. The wipers turn on, delay, and go through both low and high speeds perfectly. The problem occurs when set to the off position - they just keep going. Turn the ignition to off (as opposed to accessory) and wait a second, and you will hear a click, which is likely the relay latch arm popping up into position. Turn the key back to accessory with the switch still at the "off" position, and the wipers park themselves. Occasionally, while running in the "off" position, the wipers will park themselves on their own, but this occurs randomly after at least a minute of operation in the "off" position. The washer motor works perfectly.

Going through the service manual it asks me to find a short to ground between the wiper switch and the #1 terminal on the park relay. There is no short to ground. With the switch in the "off" position, wipers running, there is no ground at terminal #1. I determined this using a power probe and searching for ground at that terminal. All checks of wiring between the switch and terminal #1 show opens when the switch is "off" as well. Terminal #1 is definitely open with the switch in the "off" position, so the latch arm should pop, but it doesn't.

I took the motor off and tried bench testing it. In the service manual, the bench test is conducted by bypassing the pulse relay, shorting the red wire from the park relay with the pink with black stripe wire from the motor. Shorted this way, the motor works perfectly. Every time I opened the circuit at terminal 1, the latch arm popped out, and the motor parked. I put the motor assembly back on the car and with the pulse relay so bypassed like it was on the bench, the wipers parked themselves every single time. I thus convinced myself that I had discovered some zebra and that the pulse relay must be the issue. So I ordered a new one.

New pulse relay comes, with the timing circuit board, and I replace both. Put the motor back on the car and... same problem as before. After starting the wipers and placing the switch back in the "off" position, they continue running non stop until I turn the key to the off position. I then hear the latch arm click and turn the key back to accessory, and the wipers park themselves. I am at a loss.

At this point I am considering permanently bypassing the pulse relay so that my wipers will at least shut off. I do value the convenience of the delay function though, and I want to think there is a solution, so I turn to the community. Has anyone else had a similar problem with their round motor modified pulse wiper system? How did you solve it?

Update: After writing this post I added some spade connectors to the pulse relay and motor wires so that I could create a more permanent short between the red (from the parking relay) wire and the pink with black stripe (from the motor) wire. I then connected the red wire to the pink with black stripe wire and covered them in electrical tape to prevent them from grounding and installed the motor assembly back onto the car. When I tested the wipers, I found to my dismay that they were continuing to operate in the "off" position despite the pulse relay being bypassed! I was able to stop them by pulling the blue wire connecting the timing circuit to terminal 1 on the parking relay. Now the wipers are behaving themselves, but it seems that the pulse relay may not have been the culprit after all. Perhaps the timing circuit was somehow fooling the parking relay into thinking it still had a closed circuit on terminal #1? Anyway I removed the entire pulse relay and timing circuit module and now the car has wipers which will go into low, high, and park at my command, just no pulse. I am still hoping that someday I will figure out what is wrong.