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How to Connect Subs to the Factory Stereo in a BMW

1. Lift the BMWs hood and loosen the bolts that secure each of the battery cables to their respective battery terminals with a 10 mm wrench. Lift the negative battery cable from the battery and set it aside to prevent shorting the system during the installation. Lift the positive battery cable from the positive battery terminal. Slide the ring terminal from the amplifier wiring kit onto the positive battery lead. Place the positive battery cable clamp on top of the ring terminal and tighten the bolt on the clamp with the wrench.
2. Remove the fuse from the fuse holder on the ring terminal. You will need to insert the fuse as a final step so keep it handy. Insert the power supply cable (included in the amp wiring kit) into the end of the ring terminal. Route the cable through the BMWs firewall (separating the engine compartment from the passenger cabin). Move to the inside of the vehicle.
3. Pry the trim panel that spans the length of the BMWs dashboard away from the dash with a trim panel removal tool. Remove the panel and set it aside. Remove the screws beside the stereo assembly with the Phillips-head screwdriver. Remove the panel that surrounds the stereo and climate controls. Remove the two screws on either side of the stereo bracket with the screwdriver.
4. Slide the stereo from the BMWs dashboard stereo dock and disconnect the stereo wiring connectors from the back of the unit. Press the release mechanism on each stereo wiring connector before pulling them from the outlets on the rear panel of the stock stereo. Connect the stereo wiring connectors to the wiring harness adapter leads. Plug the adapters leads into the appropriate outlets on the back of the head unit.
5. Plug the RCA adapter into the amplifier leads of the wiring harness adapter. See the wiring harness adapters Users Manual for proper connection locations or follow the color-coding or other indicators on the leads themselves. Plug the RCA patch cables into the RCA adapter. Feed the cables through the back of the BMWs stereo mounting dock and down to the floor of the vehicle on the passengers side.
6. Slide the stereo back into the stereo dock. Replace the screws and trim panels onto the dashboard. Route the RCA patch cables along the passengers side of the vehicle to the rear cargo area (the trunk). Lay the power supply cable from the drivers side of the BMW to the trunk.
7. Place the powered subwoofer in the trunk. Connect the grounding wire from the grounding point on the sub to a bolt or screw in the trunk of the vehicle. Any bolt or screw less than 18-inches from the subwoofer and directly connected to the frame of the BMW will suffice. Plug the signal and turn-on lead cables into the corresponding outlets on the powered sub. Insert the power supply lead into the power input on the subwoofer. Return to the battery.
8. Place the negative battery cable clamp around the negative battery terminal. Tighten the cables bolt with the wrench. Slide the fuse into the fuse holder on the ring terminal and close the BMWs hood.