OK I can help you here as I recently did a 7K conversion in my KE30, so I had to get intimate with the wiring. :S
Plug 4 is (surprisingly) what plugs into the fuel solenoid (Plug 2), it feeds it 12VDC with the ignition on. So that clears up those two.
The nut on the alternator should be your B+ pole, this should have a thick gauge wire connected to it using a round lug (make sure the insulator ring is present on the B+ pole, the other end should be connected to your positive (+ve) battery terminal.
The green plug (plug 1) connects to your starter loom (about 4 wires), It should have a matching green plug it connect with. If not, raid a KE30 at the wreckers for the whole starter loom. I believe it's for the starter coil.