To install an aftermarket car stereo wiring harness, remove the dashboard bezel and existing stereo. Connect the new stereo to the new harness, connect that harness to the factory harness by crimping the color-coded wires together, then connect the stereo to the car.
Turn the ignition to the start position, but do not start the engine. Clear a space to work by moving the gear shifter down and lowering the steering column.
Locate the clips around the dashboard bezel and release them to remove the bezel. Use the stereo clips to remove the stereo deck before unclipping the existing harness. If the stereo deck is secured with screws, save the screws in a container. Finally, unclip the stock harness.
Strip around 1/4 inch from the ends of the wires on the new harness, and crimp them to the stock harness' wires. The wires are color coded to make connection easier. Connect the harness to the stereo and the stereo to the car before replacing the dashboard bezel.
Various types of harnesses allow the use a factory amplifier with an aftermarket stereo, or bypass the factory amplifier in favor of an aftermarket option. Relocation harnesses are used to move the factory stereo to another location while installing a new stereo. They are installed in cars that have issues with warning lights and chimes when the factory stereo is removed.