The engine harness should be sealed from the factory. you should be able to submerge the car in water and as long as the coils and intake stay dry it will run.

If it was shorting out from water in the harness then it would mean his harness is damaged from something else that is allowing the water to get in there.

It's certainly not out of the realm of possibilities... but as my fiancee says "if you hear hoof-beats look for horses not zebras"