Mobilistics™ Engine Noise Filter ...Eliminates poping ignition and whining alternator noise heard thru your radio speaker(s). Great 12vdc line filter for all types of radio's or stereo units. Use on 12vdc constant memory line OR 12vdc accessory switched line on your vehicle or boat. Use on any 12vdc device like tv, vcr, cd, 2 way radio, scanner, or monitor that is getting engine noise interference. Works on standard stereo's up to 5 amps or radio's up to 7 amp surge. Does not work on high power or amplified systems over 20 watts.