Hi guys... from Australia.
This may be of no help to you at all BUT having found an electrical 'item' attached to my Onan - then having rung seemingly every Onan dealer in Aust for info as to what it was and getting 'no idea' answers, I removed it as the Onan seemed to be ok when running.
Went to a RV show last weekend - mentioned to a local Onan rv/marine dealer, who had a display there, about the 'thing'I had removed. He knew right off what it was. Apparently with some Onan's in certain conditions spiking on start up can be bad - that's the problem could be a washing machine or whatever etc. Problem would appear on one rv and not on another even though both using identical equipment.
The problem was apparently raised with Onan USA but as it was a very isolated prob their answer was they were not going to redesign their electrics. Fair enough!.
The fix was to 'pre load' the Onan with a 500 Ohm power resistor with one end on the Neutral and the other on Active lines and the Resistor mounted to a heat sink with earth line to the heatsink. So now my 'thing' is back on the RV.
We use 240v here so I don't know if 500 ohmns is still appropriate value as you are on 120v. Also I don't know the power rating of my resistor but your local Electronic shop should be able to guide you right.
Arrow Electronics in the US has this one 850F500E 500 Ohm / 50w for less than $7.00 at https://www.arrow.com/en/products/850f500e/ohmite
BUT CHECK RESISITOR AND POWER VALUES YOU NEED FIRST!!!
Here is a pic of mine to give you some idea of what I it looks like. - MAKE SURE you protect against ELECTRIC SHOCK by ensuring the leads are well covered and the end tag connections well heat shrunk...and that its fitted well away from prying fingers, small or large.
Hope this is of some use to someone.