You've made a few incorrect assumptions!!!!
1) Heavy guage wire from battery +ve goes to one large connector on solenoid.
2) Other large connector on solenoid should go to the starter motor
4) Connect battery -ve to chassis.
5) Connect engine block to chassis
Now for some experimentation ;-
temporarily ground one of the small solenoid terminals. Using a scrap piece of wire, connect the other small terminal to battery +ve. Engine should crank. If so, make the small ground connection permanant. If not, reverse the connections and check again. If still nothing, solenoid is dead. REMOVE PLUG CAP before doing this, as if the engine starts, you have no means of switching it off!
6) The double black wire is the ignition cut off. You don't say where it's been disconnected from, but it needs to connect to the stop terminal on the engine. One of the pair goes to the ignition switch, the other one of the pair goes to all the safly switches, and it's function is to cut the engine if you get off the seat with the cutters engaged etc.
7)The wire with the inline fuse should be a fused battery feed to the rest of the tractor, and is usually connected to the heavy solenoid terminal that also has the battery +ve wire)
8) That just leaves the green wire. Since all the others are accounted for, this must be the solenoid trigger wire. To test, check for battery voltage when the ignition is turned to 'start'. Make sure brake is on, cutters are off, and there is someone in the seat before checking. If OK, connect it to the vacant small solenoid termnal.
phil_saunders@bigfoot.com
Phil Saunders, June 2008