I am in the process of converting my wiring harness to stand alone for a swap into my 1972 GMC. This is my first swap.
My question is about the wiring for the 4l60e. My motor and harness are 2002. The transmission is post 2004. The plug for the neutral safety switch/ range selector switch is the larger 11 pin plug as opposed to the 2 smaller 7pin and 4 pin plugs on the earlier transmissions. Do I have to hook the neutral safety switch up for the engine to run correctly? If I do, Can I just buy the larger plug pig tail and wire into my harness while I have it apart?

 

Yes you have to ground that neutral safety for the truck to start up.

In my 2009, after a 4L80E swap having only the neutral safety wired, the truck did start up and run but the lockup stuff didn't work. Also none of the body control stuff like fuel guage damping and auto door unlock worked until I wired up all the other terminals also.