davester

Are you sure your transfer case has "auto"? GMT800 2500 trucks didn't, and I would expect the burb to be the same.

2012 doesn't use a resistor, it has some kind of chip in the key. That's why I suggested doing that test, as IDK what kind of data is passed between the theft deterrent module and the chip in the key as part of it's authentication process.

That sounds like a "you'll have to try it and see" kind of thing. You could try it out relatively cheaply, assuming you have the two trucks already), by making a new key for one truck, but using a plain key (instead of one with a chip). Then go through the process for adding a key to the truck you made the blank for, but holding a key programmed for the other truck up to the ignition switch while inserting/turning the blank key. Then see if it works with both vehicles (one normally, the other by holding it to the ignition while using the blank).

There should be a tag somewhere on the back 1/2 of the TC, with the model number. IDK much about the specifics of TC's after the GMT800's, but you most likely want one from a 1500, as 2500/3500 will use a heavier duty one. I also don't know if GM uses different TC's for different engine/transmission packages on the 1500...

Second speed sensor? The sensor on the front of the TC, above the manual shift lever, is the 2wd/4wd mode sensor. There's no VSS sensor on the rear of the transmission (or at least, it's not used, my '06 has a plug that goes into it instead of a sensor). The harness along the transmission plugs into the transfer case harness instead of where that plug goes.

Here's a pic of the transfer case: The black plug at the rear is the VSS plug, the front, white plug is the 4wd sensor.

Having a '06 2500HD, and from doing a lot of research on how the 4wd setup works on that generation truck, yes, it is modular. The 4wd harness goes from the front diff, up to the engine fuse block, where it plugs into the main truck harness and has ground point, then back to the the transfer case, and makes a U going forward to plug into the end of the harness going to the transmission (namely, the plug what would go on the VSS at the end of the transmission if it was a 2wd truck). It plugs into the rear of the transfercase so that it can read the actual vehicle speed. If it used the transmission output shaft speed, it would need another sensor to know whether the transfer case was in hi or lo (which it doesn't have).

Speedo is run by the sensor at the back of the transfer case. IIRC from when I converted my truck from 2 to 4wd, the 2wd 4l80e has a sensor at the front and a sensor at the rear, and when converting it over, the sensor on the front is still used/plugged in, and the sensor in the rear isn't used anymore, the plug that would go into it, instead plugs into the 4wd harness, which then plugs into the sensor at the rear of the transfer case (it's basically a short extension cord to that sensor).

That was an awesome move, using the wall to turn while going full speed around the last corner. Even the NASCAR/tv computers seemed to have trouble figuring out what happened...

No, I believe autotrak was an option, you could get either a regular 2 speed TC or autotrak. It's much more likely someone replaced it with the wrong switch after it left the factory. Edit: meant to indicate autotrak was an option for 1500's and possibly 2500ld's. 2500hd and 3500 didn't have it as an option.

Most likely a p.o. bought and installed the wrong switch. 2500hd's didn't come with awd. The right switch setup just has "4x4" stensiled on the plastic instead of an awd button. I just looked through rockauto's website for the switch, and it would be easy for someone to buy the wrong switch.

Could they be some kind of shipping insert?

Are the outlets in a center console (vs the center fold-down seat)? If so, then there's a good chance someone swapped the console in, and didn't do the work of wiring up the ports. I would suggest googling for console swap videos, there's a bunch and at least some will detail how to wire them up.

Light comes on in the IP, so the switch is registering as being pressed... And yeah, it depends on current conditions if it downshifts. For my truck it seems to notice T/H being turned on right away, but takes longer or something specific to happen to exit T/H mode.

You might want to make sure the lemon law for your location still applies to the truck, as they vary by state and even location within a state.