Ahhhh! Wires...

I'm not too sure because my donor harness was cut at the firewall...BUT they didn't build the truck around the harness so there has to be some sort of sub-harness for removals sake. You might end up having to pull most of the body apart but I think even that has to be unnecessary. Don't get me wrong, it's not going to be easy, think one plug through the hole at a time possibly starting with the smallest plug.

I've looked over the FSM again and it's all compartmentalized, i.e. there is no "harness" section. Each individual component will have associated wiring in the associated section...and the wiring section doesn't have a "removal procedure"
BUT, some people sell harnesses on ebag so they have to come out in and have to be able to be replaced...keep at it and keep us posted, I'm sure someone will need the info sooner or later