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That sounds like the wire off the oil pressure switch. Check that and see if it is missing. Let me know and we can go further here if needed. All follow ups are included in our fee.
I am not certain about that. Do you have a manual with the wiring diagram? IF not, let me see if I can find one for you. See the attached link for some trouble shooting guides from Flight Systems who make a superior aftermarket board for these. http://www.flightsystems.com/pdf/onan-rv-troubleshooing-guide.pdf
See this link as well. Some good information so Bookmark this so you can come back to it again. I suspect this IS a ground lead, but tell me what it is hooked up to. And there may be another reason it isn't making any power. Be sure that the breaker(s) are in the correct position on the set. http://www.gmcws.org/Tech/dsimmons/onan/onan.html
Just checking back in to see if that information was helpful here or do you still need some additional input from me on this issue?