elec test help on Onan gen

I know there must be a common since answer to my problem.
My gen doesn't want to start. As in "starter engages-disengages" What describes my problem the best. Working my way thru the trouble shooting checklist,
(A)battery state of charge, (12.77)
(B)try starting gen with vehicle running (didn't work),
(C) clean battery cables and battery posts...Here is where I could use some help. Only one end of cable I can get to without pulling the genny. Appears the cable has a wire bracket clamp (better known as a P clamp)that holds the cable, so cable doesn't rub on other stuff I guess. I really don't want to drop the genny just to test a cable, big hassle to get it out and back in.

So I'm thinking how to test this... without the pain of pulling the genny. Thinking about running a regular auto jumper cable directly from battery to genny. In other words I'll by pass the cable being used now (that might be bad) and see what happens. My concern is the other electronics I might not see. Is there anything I could screw up doing a test like this? On genny's, the cable goes directly from battery to genny or is there anything in the cable routing such as a fuse or relay or ?


(I didn't post genny info because this is a elec test question, really not model specific).

Thanks