More than likely the oil pressure switch is grounded when there is no or inadequate oil pressure. So your water intrusion is probably grounding out that circuit somewhere. I don't have the wiring diagram but being one wire not to may other options.
titus722, Mine did the same thing once when I rode in a heavy rain. Pull the connectors at the EHC and using compressed air blow the moisture out of the plug and off of the EHC and so on. My oil light came on with the neutral light. Dried everthing out, coated with di-electric grease no more problem.
Don't forget the harness where it goes down into the connector.