Single Amplifier - Basic System

This is the simple four-speaker car-audio picture: one head unit, one 4-channel amplifier, one fused power run, and one clean ground.

Basic one-amplifier car audio system diagram showing battery, fuse, power, ground, head unit, RCA, remote turn-on, amplifier, and subwoofer. — Single Amplifier - Basic System

Fast Rules

Fuse the main power wire near the battery.
Run RCA and power on opposite sides of the vehicle when possible.
Ground the amplifier to clean bare metal with the same gauge as the power lead.
Do not use this diagram as a promise that every head unit has four clean preamp outputs. Confirm the source first.