If you make a replacement harness it would be a good idea to use the same wire colors as the original, so you will be able to refer to the wiring diagram a few years down the road, when you need to figure out what is what.

Another cause of engine fires is backfiring in the carburetors which ignites the paper filter element (often oil soaked) If you have the plastic filter box (70-72 with carbs) the whole thing goes up quickly. I know of at least two instances of this---one was put out promptly and the car was repaired, the other, sadly, was the nicest original 142 I had ever seen---a dark green 71 with less than 100K miles. I was given what was left of it afterwards and was able to salvage the trunk lid, rear bumper, the doors and most of the brake system. Under the hood was completely burned out, and the interior was heavily damaged.

I think there is less of a risk with the dual round air filters, simply because there is less to burn.