i have a 60 amp fuse on my amps only and i can blow that if i'm not carefull, i'd get your amps off you factory harness and to your batterys quick smart, best bet is
rock down to super cheap / autobarn / repco / etc
- pick up an 'Amp Wiring Kit'
comes with thick power wire, fuses, fuse holders, etc etc
wire that up to your battery,
then through a 10/15 amp on your headunit in your fuse box, run a trigger wire from the trigger out of your head unit to your amps
this means when you go to ignition your head unit switches on, which whiches your amp(s) on for pumpin tunes yo!!
if your head unit has to trigger out....
grab a 12v relay when you buy your amp wiring kit, do the power wiring for the amps straight to the battery (thats important :-) ) ...
then put the relay in so that its power is taken from a power rail, source from the ignition switch power and the output of the relay goes to your amps trigger in...
this can be done without the relay, but they're as cheap as chips and give the system a better chance for longer life, if the relay ever blows its a simple unplug 4 wires grab new relay and plug wires back in :-)
Good Luck !