 To connect to third-party FM accessories, you'll need to replace the Sonet battery pack cover with the Sonet FM battery pack cover. Remove the standard battery pack cover. Make sure that the battery pack cover lock is in the unlocked position. If it is not in the unlocked position, use the screwdriver provided with your Sonet kit to turn it counter-clockwise into the unlocked position. Slide the FM battery pack cover over the battery pack frame and be careful not to use excessive force. The air inlets of the battery pack cover should be on the same side as the coil cable socket of the control unit. Insert your three-pin FM receiver into the FM port. Follow the manufacturer's instructions to operate the FM system. Sonet will automatically detect sound signals as soon as the FM system is activated.