Hi everyone - appreciate the help and feedback. Since my last post, I did some more troubleshooting, and replaced the BCM again (now on third unit).
The issue remains and I don't have a clue where to go from here. Would greatly appreciate any pointers.
To recap, and referencing the diagram Pizzaguy provided, here is what I have done with all components related to wiper operation.
- Power distribution and MF switch: Fuse 32 is intact and provides power to MF switch. (All fuses in fuse block are intact.). MF switch correctly controls wash functions as designed, wipe function exhibits issue. With MF disconnected from BCM, the correct voltages are present at BCM C3 socket 65 (0V when MF switch "off", ~+12V in INT/LOW/HIGH positions). MF switch operation was also verified with MF connected back to BCM (using DRB III emulator for BCM Input/Output functions).
- BCM: this unit was replaced three times with similar (dysfunctional) operation of wipers. When the MF switch is not connected to BCM (i.e. removed C3 connector from BCM with all other connectors connected), the wipers still come on.
- Wiper motor: verified similar (dysfunctional) operation of a second wiper motor. Following Steve1189's suggestion, I ensured the second wiper motor was well grounded, to no effect. Park switch operation works properly (i.e. when parked pin 40 of wiper motor is ~0 Ohms to pin 41 and to case ground, open otherwise.)
- Wiring: Pizzaguy - I verified that pin 1 of the BCM provides ~+12V with respect to chassis ground (for the period of time that the wipers take the 7-8 cycles), and that pin 41 of the BCM is consistently at ground potential. I also verified that pin 41 of the wiper motor has ~0 Ohms to case ground. Pin 40 of the BCM is at +12V. (Suspect that when the wipers are parked, pin 40 from the BCM becomes grounded and completes the "sensing" circuit internal to the BCM.)
- Grounding: I checked the ground connection at C4 socket 42 to the BCM, it is fine.
Utterly perplexed. At this point I would deeply appreciate anyone verifying voltages at pins 1, 2, 40, and 41 of the BCM (wiper motor unplugged) at all positions of the MF switch.