Cat 301.8 No Start No Crank

Ok, I am in need of some real help. I have a Cat 301.8 that will blow the 10A fuse for the engine whenever you try to start it. I have disconnected the starter ignition wire to see if the starter was bad, but still blew the fuse. I have checked the fuel shutoff for a short, along with the relay in the blower motor housing. I have used a tracer from the output side to the engine fuse and only found the trace to stop in the blower motor housing. Can someone give me a hint to where to go next, and/or where the main relay panel is and where I could get a wiring diagram of at least the Starting Circuit? The only thing I can think is a rub / short somewhere in the canvas covered harness. Has anyone had this problem and what have you found.
Thank you in advance,
Tim Smith

Cat 301.8 No Start No Crank