The present invention provides a system of modular wiring harnesses that provide power from the audio amplifier to the audio source. Amplifier-end modular sections of a wiring harness may be used with a variety of amplifiers of two, four, five, or six channels. Audio source-end modular sections of a wiring harness may provide connection to one of various modular amplifier-end modular wiring harnesses. Audio source-end modular sections of a wiring harness may use a signal processor to provide multiple channel outputs from single input, responsive to the connected inputs and outputs.