Dixon ZTR 4421 no power going to starter.

Hey guys this is my first post here hoping ya'll can help me. Alright so lets get to it!
 
My cousins dixon ztr 4421 will not start when we turn the key. List of things I have checked and list of parts I have replaced with new parts from Jacks Small Engines.

1. Checked the battery, battery is good.
2. Checked all the wires for breaks, Wires are in great condition.
3. Just so I can say I checked everything electrical I checked the lights, they do not work.
4. Checked all wire harnesses. Harnesses appear to be in good condition.
5. Checked the solenoid, solenoid is good.
6. Checked all the grounds, they appear to be good.
7. Checked the seat safety switch, Safety switch is good.
8. Replaced the key switch, the circuit breaker and the relay. The others were rusted and the circuit breaker was broken.

After I installed the new parts it still wouldn't attempt to crank. I am however able to fire it up if my cousin is on the seat and holding the key in the on position while I attach the negative clamp of a battery charger to a motor mount bolt and touch the starter bolt with the positive clamp of the charger Also at this point I should also state that I checked the pto switch the electric clutch came on and the blades engaged, and after that he is able to turn it of using the key switch. It was getting late so he said he would just crank it that way until I can figure it out so he went to mow the next day and the blades wouldn't engage. I will be going over there Saturday to try and figure out what is wrong with it. I'm really scratching my head on this one. Any help would be greatly appreciated. Thanks in advance.