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I am having trouble with my 2 speed in my 1972 F600. There is a black wire that attaches to something right behind the speedometer that clicks like a solenoid. What is this? Can anyone tell me where the wiring harness goes? There are three wires to the selector switch and these go into another harness that contains that black wire. Can anyone provide me with a schematic of the wiring? Thanks
2-Speed axle wiring: I have scanned the 1973 (which, while different, should be similar to 1972) wiring diagrams for F500-F750, and you can get them from the link posted in the first post of this thread. I don't want to post the link here, because if it changes, I want to be able to change it in one place, not 50 different threads.
It's six large pages.
It shows power from unfused Ignition Switch (Page 3) via wire designation 297, color Black w/Green stripe
To internal harness connection S-701 (Page 4)
Splitter connector C-1001, probably in the dash (Pages 4 & 6)
Protected by Circuit Breaker CB-2 (Page 6)
To the gearshift switch via wire 142 Green (?? There is not "GR" in the color table on Page 1. Gray = GY, so I'm guessing "GR" = Green ??)
Finally, to the axle motor via wire 141 Black (which also splits off to the speedometer cable gearbox) and 143 Red, via several connectors along the way.
Here's a cut down/marked-up Page 6 that shows the meat of the 2-speed motor wiring:
IDK why this shows the fuse panel on the left side; every one I've seen is on the right kick panel.
Note the motor's ground location on the frame, near washer 34940-S. That ground, and the two connections next to it, form "connector C-1010" and would be an excellent place to check. Ground connections like that, exposed to road conditions, are a great place to begin. You have power from the gearshift switch to the speedo gearbox, so I'd check downstream, and that would be my first choice. On the frame, directly forward of the shift motor.
Got everything fixed. Found one broken wire (the green one) in the harness at the bottom of the shifter. Purchased a new harness from NAPA and it works fine. Thanks to everyone who responded.
