Craftsman Lawn Tractor Won't Start?

I have a Craftsman lawn tractor 18.5hp 42" deck. Model#917.275760. The tractor will not turn crank over, the battery is good, 12.5 volts, 95% charged and load tested to 11.075 volts. I have changed all four safety switches, the ignition switch, the starter 4 post solenoid, the starter, and the ignition switch. The mower will not crank over, after all these new parts. I have visually checked the wiring harness, for burnt wires, corrosion, and loose connections. I found nothing that would keep the motor from cranking. I have checked for any diodes, found none in the electrical systems. There is a protection wire loop p/n 141940 shown in the wiring diagram. This diagram is for this model tractor. Where would this wire loop be located? I'm not sure what this loop would even look like, if i saw it. When I stated that I checked the wiring harness visually. I also used a multimeter and a 12 volt light tester. Can anyone inform me, what the no crank, problem could be? Also, does this protection wire loop replace a diode? Why didn't Craftsman use a fuse in the wiring instead of a protection loop?