Ok I know enough about amps, and hook ups, I have a small 4 channel JBL amp, it pushes 18 watts rms @ 4ohms x 4, it already has a small power, ground, and remote wires coming out of it, like a head unit, I dont need the run its power from the batery directly do I like a normal amp? I can hook it up like a regular amp right? and wat kind of fuse should I use? 20A? or more? or less?

Also, the small amp is going to power my door speakers, should I just run the speakers to the radio instead? seeing how the amp isnt going to be doing alot?