Disconnect the vehicle battery
Identify the subwoofer terminals
Identify the amplifier output terminals
Match positive to positive
Match negative to negative
Use the correct wire gauge
Strip the wire ends
Connect the speaker wire to the subwoofer
Connect the other end of the speaker wire to the amplifier
Tighten all terminal connections
Secure the wiring away from moving parts
Reconnect the battery
Test the subwoofer at low volume
Adjust the amplifier settings if needed