Find a safe place to stow your crossover.

Protecting the crossover

Make sure you house the crossover in a dry place, such as in a hollow space behind the plastic door panel. If you must mount it on the door metal, wrap the crossover in a plastic bag and tape the openings to keep it safe from moisture.

The crossover should be secure against vibration. Merely placing the crossover in the door or kickpanel leaves it likely to be tossed around. Also, as with the speaker installation, you'll want to make sure the crossover does not interfere with any moving parts. Put the crossovers through the same rigorous tests as you did the speakers, specifically with respect to window and door mobility.

How your system should connect: receiver to crossovers, crossovers to speakers.

Wire networks

Since you'll most likely install the components in new, unwired locations, you'll have to spend some extra time wiring them. Component speakers also come with external crossovers, so the wires running from the receiver must first be routed to the crossover, and then to the individual woofers and tweeters. If connecting an amplifier as well, the amp should be wired between the receiver and the crossover.

If you're connecting an amp, make sure you connect the receiver to the amp first, and then connect to the crossovers.

The rubber boot that protects your door wires' journey to the dash is a great place to house your speaker wires.

Wiring through existing door boot

Once you've found the best location for your component system, you'll need to hook it up. Fortunately, most cars sport a rubber boot that connects between the door and the car body. Using this boot as a conduit, run your speaker wires off the door, underneath the kick panels, and to your receiver or external amplifier. You can easily do this by taping the wire to a straightened coat hanger and fishing everything through the interior panels.

Test-driving your system

At this point, you'll want to test your system before fully reassembling your doors. Loosely attach the door panel to the door, barring the window crank. If you chose to bottom-mount your speakers, mount your speakers in the door before hanging the panel. Holding the speaker in its new hole, mark the screw holes; then remove the speaker, and drill accordingly.

Pull the wires through the door and attach them to the speaker. As long as you're consistent, it does not matter which terminal you use as positive and negative. Next, hang the speaker in the door. You may need to use "speed" clips (often provided) to give the speaker screws extra support. With all speakers in place, you can listen to your stereo to make sure it works to your liking. Once you're satisfied, finish reattaching your door panel.

Cutting a wire hole

If your car doesn't have a rubber boot, you'll have to drill a 5/8" hole to string the wiring through. Before drilling, make sure the hole will have access to the desired speaker location, as structural steel sometimes blocks the edge of the door. Cover any sharp edges of the hole with a rubber grommet, several layers of electrical tape, or some flexible tubing. Make sure the door will stay open all the way, and that the wire will not get pinched by the hinges or door jamb. Once you finish drilling and cutting, vacuum all metal debris before finally installing the speakers to prevent rattling or shorts.