I am going to do an install in a car that has a factory radio, my only question is about the remote wire, since the factory stereo doesn't have a remote wire on the back of it, can I just hook it up to the ignition wire so that when the car is turned on the amp will come on, and also should I put a fuse the line. I read this somewhere, but you never put a fuse in the line when doing any other remote wire that I know of anyway.
If you hook it up to the wire that powers the radio when the switch is on, that should work just fine. It cuts the amp on when you are going to be listening to music so it isn't on all the time, just like your radio. There shouldn't be a need for a fuse in the wire since it isn't carrying that much of a current and it will only have current running through it when the radio is playing, not all the time.
mmmm no. the +12VDC line that powers the factory radio is a switched ignition and 12V constant depending on which wire you choose. One is also the illumination wire. If you're tapping into the factory stereo, ahve you considered using something like the JL Audio Cleansweep? This provides clean pre-outs from a factory system, and provides a remote trigger line. Another option is an interface like the PAC OEM1.
Otherwise, yes you'll have to use a switched ignition line, and the one behind the radio will work, but may also induce noise. The problem is that line isn't isolated or filtered, and if it is run in the car anywhere by the ignition wiring, you're looking at EMI. Alternator whine, popping noise, etc.
amplified subs like the Infinity BassLink and SAS Bazooka (amp'ed) have the means to tap into the factory rear speaker wiring to get the signal, and also use signal sensing to trigger remote on/off for the internal amplifiers. They don't actually need a remote trigger in that case.