I agree..if that wiring harness is burnt you will have a heap of parts not working.You are being scammed. Don't fall for it. Find a real, honest mechanic who knows what he is doing - I bet he can fix it at low cost. It's highly likely it's a simple connector or similar issue. This is a prime example of how Dealers operate. They will break a bolt off in the frame and then say you need a new frame. I wouldn't trust any of them, at all, ever. They will also cover for each other. If you were here, I could point you to the guy who can fix you up. Look for a good local automotive electrical shop. There are a couple of those here as well, though my guy is so good I don't need them.
Heck, if I had to I'd go to a wrecking yard and get the fuse box along with the cut off connectors and pigtails to it and splice it in myself. If that's even the problem. There's at least a 50-50 chance it isn't the problem. The thing is, most dealers don't even have a real mechanic any more, they just have techs who are trained to operate the diagnostic machine and then just do what it recommends. You might just have a loose or dirty pin in a connector. It could be that simple. Hence the expression - hard to pin down. I'd bet real money you can find someone who can fix it right for much less money.
If you can see a burnt section on the fuse box then OK go and get a used part and cut the wires... one for one..and splice in the used unit be sure to work colour for color
Get it to an auto electrician..6 hours labour is a rip-off. The harness is a plug for plug fitting.