by wiring kit do you mean the amps power kit? some of which will include speaker wire for the subs anyway usually your amp will come with instructions that tell you what the minimum gauge is the amp will accept for power, this is the gauge power and ground cable you will want to get maximum power to the amp and to prevent overheating issues, typically amps under 400 watts rms power will do fine with 8 gauge, amps 400-1000 rms will use 4 gauge and 1000+ will use 2/0 gauge wire, for the subwoofer speaker wire you can never go too big gauge only too small, a kicker 12 gauge speaker wire will work for almost any application
