Audio Wiring / September 7, 2018 / Raquel Dufour.
You don’t want to route signal wire next to power wire because that could result in noise entering the sound system. If power cable and signal cable must cross, cross them perpendicularly. Use well-shielded RCA cable. It will help prevent noise from entering the sound system. Ground the radio to the chassis. Connect the antenna to the proper antenna input on the radio.
Before you do a parallel hook-up on an amplifier, make sure that the amp can take the ohms load that will result. Find out what ohms load the amplifier is stable at and then choose speakers with the appropriate ohms rating so that the hook-up will ensure that the ohms load is within the capability of the amplifier. Generally speaking, most midrange, midbass, and tweeters you use will be 4-ohm rated. Most subwoofers you use will be 4- or 8-ohm calculated.
Use a self-tapping sheet metal screw and drill through the metal on the backside of the seat or into a part of the trunk floor NOT IN CONTACT with the gas tank. Remove the screw, and grind off any paint around this area. You want a conductive connection to the chassis. Drill the screw back into the hole you created, this time with the ground wire attached. Use some silicone sealant to seal up the bare paint area to prevent rust.
Route the signal cables (RCA cables) on the driver’s side of the car from the head unit to the amplifier. Ground the amplifier to a clean metal surface on the car’s chassis. The ground should be no more than 18 inches from the speaker. The ground cable must be the same gauge size as the power cable used.