You have to ask yourself what makes more sense. You can certainly cut out individual burned up wires and replace them with the same gauge wire. Or you can just get the full harness and replace the whole thing. It just all depends on whether you want to deal with splicing in a bunch of wires, it requires a lot of patience. I've done it before on one of my cars and its not very fun squeezing yourself under the dash to get to them. But it did make the harness last long enough for me to get the money together for a full front to back new one. If money is tight then it might make sense to fix it and then replace it when you have the means. But if you do have the cash, I wouldn't bother with fixing it.