2002 3500 I have a transfer case plug but I have a two-wheel drive truck

So I bought a truck with a blown engine I got a short block and I've got it back together and hooking things back together I find I have a plug that I didn't have anything to plug into. This turned out to be a transfer case plug. Dtcs are telling me that there's a communication problem with the transmission. I'm wondering if what it's referring to is really the transfer case it's not there the truck doesn't shift it's in limp mode it will periodically act like it's not in drive or reverse, but putting it back in park fixed this.

Does anyone know if the transfer case is in the chevy.build? Unselectable?

Do I need a new wiring harness?