Transmission wiring harness
 

I have a leaking reverse switch so I've purchased the switch, drained the fluid and then realize that the previous owner must have not know how to route the wiring harness (he replaced the engine) so everything is spliced together under a mound of electrical tape.

I found something called a transmission wiring harness at onlinemazdaparts so I guess it is a separate piece from the main harness?

Is the transmission harness something easy to replace as one piece or should I take to a professional? I have some basic maintenance skills but am not a mechanic by any means.

There is no separate transmission harness. It's part of the engine harness, there's only 4 plugs(2 white, 2 black) very easy to sort out.

Guess I am lost here. Is the wiring to the transmission part of the main harness or something that plugs into it? It looks like the o2 sensor is plugged into it also.

Sorry for the confusion but can't find any pictures of what it looks like.