the remote (amp turn-on) wire, can be hooked up to accessory(red wire on aftermarket radio harness), if there isnt a blue/white (remote turn-on) on the aftermarket radio harness. There is no reason to go and test for power at the fuse box; while that works - -if he doesn't know about amp installation then he most likely doesn't know how to test for power. red wire on aftermarket harness is thesimplest way to go if you don't have an amp turn-on wire.

 

your subs should be plugged into the amp via RCA's, and besides that, thats the only connection between the HU and Sub amp... Then you have your 12v, ground and signal wire, and then your outputs, its easy. But i didnt read the whole thread so. Goodluck