The old Onan ladder diagram troubleshooting
service manuals can sure spoil guy. A Onan service manual was actually a real Service manual.
Just walk you right thru step by step troubleshooting. Heck Ronnie Milsap could use those to locate and repair Onan electrical and mechanical. Some of Onan's Service manuals were two separate manuals for electrical and mechanical.(and priced within reason)
I was into a Electrical issue on a piece of equipment awhile back and the
service manual was worthless for troubleshooting the electrical control circuits and not all that great for mechanical.
Service section would just get you in far enough to wonder where that wire comes from and the correct wiring diagrams color code did not even match the equipment.
I do believe in Service manuals, but now days I'm not surprised when they are weak on service info and not much better than a owners manual.