Place Purchaced: ebay
Price: $12.xx

Purpose: to eliminate ground loops and engine noise that is being emitted through the speakers of an amplified system.

They worked really well once I figured out how to install them (instructions were kinda vague).. It eliminated my annoying alternator whine emitted by my speakers completely!

I would recommend to anyone.

Installation (since the directions were stupid):
Plug the RCAs from the GLI into the back of the headunit and plug your RCA cables into the GLI box. There are two brown wires that come out of the GLI (this was my downfall).. The brown wires MUST be connected to a piece of metal on the HEADUNIT (not the chassis of the car). It will only work properly if you do this.

I originally plugged the GLI into my amp and the rcas into the GLI and if muffled the output terribly. You could plug the GLI into the amp and plug the RCA into it but you would have to somehow extend the brown wires all the way through the car to attach them to the headunit so its easier if you mount the GLI behind the headunit and not on the amp. I hope this wasnt confusing for you all but I felt it necessary because it took me like an hour before I realized that it didnt work right until I attached the brown wires to the headunit.