Here's the problem:
The wiring harness in the engine compartment (the 3 wire group) is set up for 4WD. The cab side of the harness (the 2 wire group) is set up for 2WD.
The primary difference is that a 4WD TCC control system incorporates a 4WD relay. The relay disables the TCC unless the transfer case is in either 2WD or N.
But that circuitry also requires that the transfer case have a 4WD lock-out switch which activates the 4WD relay. Also, not necessary but useful, are a couple of lamps (4WD indicator light on the dash and transfer case shifter illumination).
On the other hand, the only component on the cab side of the 2WD circuit is the brake switch (same part as used with 4WD).
So there are several ways to reconcile the differences between the two dissimilar circuits (that I can think of). Here they are - ranked from hardest to easiest:
1. Locate/purchase/install all the required parts to allow for the 4WD lock-out feature (relay, relay base, TC switch - and the indicator/illumination lights) and fabricate your own 3 wire harness to allow it to link up with the engine side.
2. Find a complete 4WD set-up (cab side) at a junk yard, carefully remove it and install into your cab.
3. Leave the cab wiring as is and just remember to take the transfer case out of 4WD if you intend to drive faster than 45 MPH (the approximate speed at which the TCC engages). Requires an easy modification to the engine side harness (cut the LT GRN and the BLU/BLK then splice them together). The brake switch will still disable the TCC as designed.
The light green going back into the cab is to the test connection and isn't necessary.
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I would pick option 3.