I have the FULL Ford Service Manual set. There is just ONE wiring diagram for both the gas and diesel. The ONLY difference is the diesel has a switch with four connections, the extra one is for the thermostart (glow plugs) needed for the diesel. One is used only for the "accessories" (dash gages) on the diesel but is the one also going to the coil in the gas tractor, as well. The other ignition switch connections are the one to the starter soleniod and the one that goes the the battery post on the regulator and to the light switch. Note the light switch is ALWAYS connected directly to the battery - it does NOT go thru the ignition switch.
I had to rewire my 3000 (same as the 2000 just a HP derated tractor for the "low end" of the thousand series) because the wiring was a mess - just enough to start it and keep it running, no charging of the battery or readings on the instrument gages. I ran the new wires over the gas tank to the starter soleniod. Mice decided to make a nest on top of the tank and chewed thru the insulation on both wires causing them to short. One day when I started the 3000 the starter would not stop running!! Luckily I had put arc welding disconnect plugs in the battery cables so I could remove the battery and lock it up when I went back to the city. So was able to disconnect the battery and stop the starter before any damage was done.