In the manual I have it shows a ground lead attached to the radio casing, pg 8-54. You did say you have nothing on the display right? no power at all? If that's the case, then it's not the mute. All though I don't think it has a mute mode. Don't have my bike right now to check it out, it's in the shop. The CB is under the trunk. Worth checking the wires under the seats.