First thing is to find a power lead that is grounded, you don't need to know where it goes to start, just ground out one probe and put the other probe on the wire end. ( disconnect the + side of the battery ) Once you find a wire that you think has a problem, then try to find the other end and make sure the invisible water goes all the way through using the same method but isolate both ends and then double check the grounding issue. If the water goes through and is not spilling out it's not your problem.
I'd key on anything in the bundle running through the steering neck area and the headlight wiring in particular since you mentioned that it was a problem.
This is just a matter of elimination, you may get lucky and find it first oooorrrrrrr not so lucky. Thankfully the harnesses aren't that complicated on a dirtbike.