Thank you for viewing. This is used to eliminate alternator noise that can interfere with the audio signal lines (RCA pins) of a car audio system. It's a rare item, but it was quite popular back then. It's quite old, but it was working without any problems until it was removed. Please judge the condition from the images. Please refrain from purchasing if you are looking for a perfect new item or if you are overly sensitive, to avoid any issues. Shipping is free. Please understand the above and consider purchasing if you understand that this is a used item.