New Wireing harness?

[Deere Jon]

My truck has 300,000 plus miles on it and has at least another 200,000 left in it. I plan on owning this rig for a long time. I get sick and tired of fixing the tail light problems specific to my truck. The rear section wire harness is completely junk. Can I buy a wire harness for the first gens from dodge or after market, and is it at a reasonable cost? Has anyone else replaced their wiring harness? How is the harness connected inside the cab, Is there a connector in there or does each individual wire get plugged into the fuse panel or somewhere else? Thanks for all your help lately. Jon