A couple of weeks ago, we got 8 inches of sleet/ice/snow, and I needed to engage the rear locker (and front locker too) to back out of the driveway to the street. The locker engaged normally, when I got to the street, it wouldn't disengage. No change at all from turning the switch off. Turned it on and off a few times,. nothing. So I just drove it to work (it's not all that far) with the locker engaged.
A few days later the temps got a little nicer (around 20 degrees) so I tried some troubleshooting. Both fuses involved (4WD and GAUGE) were good. Pulled the kick panel and did some basic multimeter tests there, all seemed pretty OK for the locked status. Pulled the carpet under the seat and tested there, same results. So I jumpered 12V+/GND to the M1/M2 wire pairs and could hear the actuator locking and unlocking. Left it unlocked, plugged everything back up, same results as before - it would lock (sort of weakly?) and wouldn't try to unlock. It still being cold and miserable, I didn't want to lay under the car in the snow much, but I did briefly hop under and make sure the plugs were still in place on the actuator and lock switch. And jumped(!!!) to my first conclusion - that the ECU was bad. I didn't think it was the wiring because it would lock and unlock when jumpered directly, and I replaced the harnes from the body to the axle only 2 years ago. I didn't think it was the actuator because it would lock and unlock when jumpered (I jacked up a wheel and it was actually locking and unlocking). A somewhat weak lock, and no attempt to unlock when everything else is OK? Must be the ECU!
So I ordered one, left it manually unlocked, waited 5 or 6 days for the ECU to show up. Plugged it in and...... no change at all. Exact same results. A weak lock attempt when it was unlocked, no attempt at all to unlock. I guess it's not the ECU. (I looked my ECU over carefully for bad solder joints, common on old electronics, no issues). At that point all the snow was in the process of melting, miserable to crawl under the car (it doesn't fit in our garage - too tall) so, despite jumping tot he wrong conclusion once, I jumped to another, bad actuator. And ordered off a new actuator, because I'd like the locker to be reliable. We do some fun stuff out in Colorado and Utah every year where that locker really needs to work.
So waited another 4 or 5 days for that to show up. By this time the snow was mostly gone. So I crawled under the truck, unbolted the locker wiring harness brace on the actuator, unplugged the 2 connectors (which is a blind and awkward PITA) and pulled the 22 month old harness down. I was going to plug the new actuator in it and cycle it a few times before taking the old one off and replacing it. And finally, belatedly, after way too much blind/dumb parts cannon firing, I found the actual issue. Some broken and damaged wires.
I replaced it a couple of years ago because the wires broke somewhere in the middle where they flex every time the axle moves. And they only did that after 20+ years of flexing around. But this time, I'm not entirely sure what happened. The wires don't really move near the actuator plug, the harness has a brace bolted to the actuator further back - no movement between that and the plug. Not mouse chews, the wires look like they were pinched. Most have some damage to the insulation, and one was completely severed and missing about 1/4". I (belatedly, again) presume that is the unlocked limit switch inside the actuator. With the wire broken, the ECU assumes the actuator is already unlocked, so it won't try to run the motor for the 4 seconds like normal. The lock limit switch wire is intact, so with it unlocked, the motor will try to lock it. I think the weak locking from the dash switch was perhaps because of damaged but not completely severed M1/M2 wiring, resistance dropping voltage enough that it was weak through the factory wiring, but strong enough when jumpered directly from a spare car battery at the rear seat.
So yeah, 2 bad hasty parts bought before getting to the real problem.
There's nothing around that area on the truck that I could see that would hit it. The parking brake cable is above there, but it moves with the axle. About the only thing I can imagine is that a rock got flipped up on the axle at some point, bounced off the wires and fell off again?
