Locate the amplifier. It is usually located under the passenger's seat, but its also behind the passenger seat in some cars.
Disconnect the power and speaker wires from the amplifier.
Connect the power and speaker wires directly to the head unit.
Turn on the head unit and test the speakers.
If the speakers are not working, check the connections and make sure that the head unit is turned on and the volume turned up.
Additional Note:
Some factory amplifiers have a built-in signal processing (DSP) feature. If you are bypassing the amplifier, you will lose the signal processing. This may affect the sound quality.
