YADLT (Yet Another Door Lock Thread)
 

I did search and read, but my problem has elements of several other complaints plus a callback to my thread about burning up the rear hatch cable harness.

Truck is 2000 Ltd with 238,000 miles

So, to recap, a couple of weeks ago while driving home at night, I smelled strong burning wire insulation odor. No visible smoke, but the odor was overwhelming
Got home without fire, but was scared of a burst of flames for the last fifteen minutes of driving. Upon parking, I disconnected the battery and turned in for the night.

Problem turned out to be wire/insulation failure in the rear hatch harness, where the common wire breakage occurs. Best I can tell, no fuses popped, but there was severe wire burning:

https://kkoop.com/Images/T4RWire2.jpg

I got a couple of harnesses from salvage and spliced in good wire, cut from the hatch end to the connector pin, so only one splice per wire. Finished repairing all the damage - which turned out pretty good - and installed the harness.

Rear window, brake light, and wiper all work now.

Problem is the locks don't work. They got squirrelly when the near-fire happened and I was hopeful the repair would bring them back online. Here're the symptoms:

• Pressing driver arm rest button or keyFob "Lock" button locks the driver door only.
• Pressing driver arm rest button or keyFob "UNLock" does nothing; no action no sound.
• Pressing KeyFob "Lock" button does not cause a beep.
• Pressing KeyFob "UNLock" button beeps twice, as normal, and flashes the lights (but, again, does not unlock anything).
• Pressing the passenger arm rest button "Lock" locks the driver side only.
• Pressing the passenger arm rest button "UNLock" does nothing, no sound no action.
• Manually unlocking the driver door with the key works, but am unable to lock the door - the key won't turn clockwise; like the tumbler is jammed.
• Passenger door can be locked or unlocked with the key
• Locking all four doors by manually pressing each lock-button on the sill, and then locking the hatch door with the key actuates the alarm.
• Unlocking the hatch with the key disables the alarm
• Unlocking driver or passenger door with the key disables the alarm.
• All windows work from the driver arm rest buttons.
• Hatch window works with the key, and from the dashboard button.

Any input on how to troubleshoot this is very much appreciated!

—Kel

Does the 1999 have the fob control in the rear door hatch? I am suspecting meltdown may have affected that module too. The early years its under the drivers seat I am not sure if its under the seat or in the rear hatch on a 1999.

That were I would start testing anyways. Verifying its working properly. As the fob controls go through a controller.

I wondered about that. There is a controller-looking box inside the hatch door, to which one end of the burned harness attaches, and I was afraid it may have been damaged by the short and resultant astronomical currents.

I was hopeful that, because the window, wiper and brake light work, the box was okay and doing what it is s'posed to.

I meant to grab one when I was getting salvaged harness cables, but forgot. Guess I'm heading back to the pick-it yard.

—Kel

The '99-'02 rear hatch houses the keyless entry receiver, which also controls all back door functions (and communicates to the body ECU via an early-style not-quite-CAN bus).

With the rear ECU unplugged, the main 4-doors should still lock when pressing the driver or passenger lock buttons, so I suspect there is still some issue up there.

The alarm will not activate if the body ECU does not receive the 'ok' signal from the position sensors on all 4 door locks and the rear hatch lock via the communication bus (nor will the single-beep activate on non-alarm trucks).

Since the rear window works from the dash button, the communication bus is working, so that's a plus. I'd track down possible issues in the driver's door harness and/or master switch panel. There may have been a related issue that happened up there at the same time.

-Charlie