Installing a subwoofer and amplifier, although often time-consuming, is simple in a Volkswagen Jetta MK III. The interior and, more importantly, the way the interior comes apart, gives even the novice car enthusiast an easy platform to create a bumping car stereo system. These instructions will guide you through the process of installing an amplifier and subwoofer into the interior of your VW Jetta MK III.
Disconnect the car battery and place the subwoofer and amplifier in the trunk.
Connect your subwoofer and amp together using speaker wire, making sure to properly connect the positive and negative terminals.
Screw the amplifier into the trunk to keep it from moving while you are driving.
Fold down the back seat and lift up the seat cushions. This is where you'll ground the amp.
Use a monkey wrench to unscrew the nut holding down your seat belt buttons and connect the ground wire.
Screw the nut back on and connect the other end of the ground wire to your amplifier. Leave the seat cushions off for the next part of the installation.
Remove the head unit and open the passenger doors. Look near the floor to see plastic covers lining the area between the carpeting and the doors.
Remove the screws holding the plastic pieces in place using a Philips head screwdriver and remove the plastic pieces. This is where you'll run the RCA and power cable from your amp to your head unit and car battery, respectively.
Run the wires from the trunk beneath the back seat cushions and through the area where you removed the plastic covers near the doors. Peel back the edges of the carpeting in the front seat and pull the wires through the area. You'll later cover the carpeting over the wires to conceal the installation.
Run the RCA cable from beneath the center dash up through the gap left by the head unit. This can be tricky and is easier done with two people, one acting as a guide for the wire. Sometimes pulling the wire through with a coat hanger can save time. To do this, push a straightened coat hanger through the hole until it reaches the bottom, where you can tie the end of the RCA cable to it. Pull the hanger and the RCA cable up through the head unit gap.
Connect the RCA cable into the back of the head unit and reinstall the head unit.
Pull the power wire from the passenger's side floor to the driver's side floor. There is a gap underneath the center dash to do this.
Peel back the edges of the carpeting on the driver's side floor and look for a hole to feed the power wire through to the engine bay. Once you've found it, connect the power cable to the battery. Be sure you've installed the in-line fuse holder to prevent fire in case the power wire shorts out.
Seal the hole that you ran the power wire through to prevent water from seeping into the interior and shorting out the wire. You can use caulk or any other electrical-safe sealant.
Fold back the carpeting, reinstall the plastic coverings near the doors and put the back seat back together, and the installation is complete.
