Ouch, That's pretty tough job. You need to first get the machine completely stripped down so you can see everything. Then get all the cable ties off the original harness. Taking lots of pictures of the routing will help. I lay the main trunk in first and work toward the peripheries double checking everything as you go. You also need a big tube of dielectric grease so you can seal all the connections as you go. And a big bag of cable ties.
Why are you replacing the harness? It may seem like the easy way to cure an electrical gremlin but I will ONLY consider total replacement as a last resort. Its NOT easy.