Ok guys here we go, I have a 2003 Chevy S10 extended cab pickup, I kept the factory headunit, and using the high level speaker inputs to run the speaker signals to my amp (JL 360/4) Using speaker wire, I spliced the high level speaker inputs off of the harness wires that connected to the factory speakers in the door and dashboard and using more speaker wire I ran the new speakers that I installed directly to the amp speaker inputs. Im using a small powered subwoofer box in which I tapped into the rear speaker high level speaker inputs off of the same wire that I used to run into the speaker amp. I ran the power wire and remote wire (which is wired off of the fuse box) on the passenger side of the vehicle and ran the speaker wire for the amp and high level speaker inputs on the drivers side of the vehicle, and made what I believe is a good ground in the middle of the vehicle in the back off of a bracket that is used to hold the jack in the truck. After I wired it all up, the system sounded good, no interference, clear highs, nice mids, and deep lows. With the music playing, I slipped some wood behind the carpet behind the amp and began screwing it in with a manual screwdriver, while I was doing this I began hearing some distortion and static coming thru the speakers that I had installed, and I turned off the car and turned it back on again. After I turned it back on, there was an amazing amount of interference, and its driving me NUTS!!! Sorry for the long post, but can anyone…ANYONE help me!!!!!
the ground needs to be made to sanded bare paintless metal the power line has to go directly to the positive terminal of the battery, not to the fuse box, and it has to be the same gauge as the ground wire, which in your case should probably be 4AWG between the 300/4 and the powered sub. make sure the gain on the amp and powered sub are turned down since having them set too high will cause feedback and noise. instead of using high level inputs for the amp(s), consider getting a PAC OEM1 type interface that uses a T-harness to tap into the radio wiring behind the head unit, and gives you RCA line-level outputs for running signal to the amplifiers. It also gives you a remote trigger feed to turn them on. Using the fuse box for remote trigger is also a cause for noise. your ignition system uses the same fuse box, and the inductance and capacitance in the wiring at the fusebox is a recipe for disaster.