The PAC LC-2 is one of those essential pieces if you're adding an amplifier to your car's factory stereo system. Basically, it takes the speaker-level signals from your car's stereo and converts them down to preamp levels that your amplifier can work with. The cool part is the dash-mountable remote control - you get this little knob you can mount somewhere accessible that lets you adjust the signal level going to your amp without having to dig into your trunk or under seats. It works with most factory and aftermarket radios, which is super handy. This is particularly useful when you're adding a subwoofer in the trunk - you can fine-tune the bass level right from the driver's seat. The installation is pretty straightforward if you're comfortable with car audio wiring. It's been around for years because it just works reliably. If you're upgrading your car audio but want to keep your factory headunit, this little device makes the whole process much smoother and gives you that control you'll definitely appreciate later.