Bigger issue is the black wire goes to the choke thermostatic pull-off. It pulls the choke partially OFF when the engine starts. I can't really see, but it appears that electrical terminal is gone from the pull-off. Those things are very rare to find.
There is a long time GMCer in Nanaimo by the name of Gordon Reid Nichol. He runs a FB page called "Classic 1973-1978 GMC Motorhome parts". He might be the best local to you source or he might know someone with a parts Onan.