Our Itasca's Onan 4K inside start switch by the galley stove is a rocker switch. Rock it one direction and only the Onan fuel pump runs to bring in fuel - I can hear it clicking as it pumps. Rock the switch the other way and the Onan starts.
I wonder why all the RV manufacturers don't use Onan control remote switches that allow you to power just the fuel pump for awhile before attempting to start the generator?
By the way, this rocker switch IS NOT labeled clearly so that this fuel pump only function it provides is not obvious. We owned our Class C for awhile before I discovered this. I wonder if the OP's inside Onan start switch isn't the same?