First let me give you my standard reply, then you can decide if it has merit in this case. Beginning Electrical students almost always guess to "run a new wire" for this type of problem, but the fact is you need to find the break or short so you can see what caused it and if any other wires are affected. For example, on some cars a plastic clip can break and let a wiring harness fall down onto hot exhaust parts. When the insulation on the first one melts through, that wire will be shorted to ground and cause a problem. If you were to just run a new wire, you'd have to cut the old one off on both ends to remove the short, but how long will it be before the same thing happens to the next wire? That second or third wire could leave you stranded many miles from home, ... On a Saturday night, ... After midnight! If a mechanic was responsible for replacing that first wire, you can be sure he's going to hear about you having to walk home.
In this case we know what probably caused those wires to melt, but unlike other wires developing the same problem due to hot exhaust parts or sharp edges on metal brackets, it's those melted wires that could have melted into other wires for other, totally unrelated circuits. This is where you can have things like the wipers turn on when you turn on the head lights. If those other wires haven't melted together yet, there's a good chance they never will at this point. You might be able to cut the melted wires at both ends and run replacement wires. If other electrical problems develop in the future, you'll have the advantage of knowing where to start looking.
Many years ago you could run to a salvage yard too to find a replacement harness. There were a lot of them that were just a few feet long and easy to replace. Today, however, it is common for harnesses to go from one end of the car to the other and cost over a thousand dollars for new ones. Those can take many hours to replace. You're better off repairing the harness. Replacing those can lead to forgotten screws and mis-positioned parts that cause rattles and other annoyances.
Saturday, October 17th, 2015 AT 9:27 PM