Plug 1 is the plug you would use for dealer mode or connecting a Yoshi box or such, it's the ECU connection plug.
Plug 2 is a jointing 'block' for several earth wires and not really a plug.
Plug 3 I'm not 100% sure, but I think it is used for the Suzuki/Acumen alarm connection. Greywolf can probably confirm/correct me on that.