[. . . ] Connect it to the remote turn on lead of the head unit or signal source. 4. GND Connect this cable directly to the frame of the vehicle. Make sure the metal frame has been stripped of all paint down to the bare metal. [. . . ] Subsonic Filter Control This control can filter out unwanted low frequency from 10Hz (OFF) to 50Hz. This function will increase the power handling of your woofers. 11. Bass Boost Level switch This switch can boost bass level by 0dB, 6dB or 12dB. Power Indicator This LED will light up when amplifier works properly. 13. Protection Indicator The red LED will light up or be flashing if there is a fault presented to the amplifier. Please disconnect the amplifier and resolve the fault before reconnecting the amplifier. PANEL LAYOUT Fig 1. S550. 1D/S850. 1D/S1300. 1D/S2000. 1D Panel layout 12 13 7 5 6 11 8 9 10 PANEL LAYOUT 1 2 3 4 INSTALLATION PRECAUTIONS Before you install the amplifier, investigate your car's layout very carefully. Take special care when you work near the gas tank, fuel lines, hydraulic lines and electrical wiring. Before making or breaking power connections in your system, disconnect the vehicle battery. Confirm that your head unit or other equipment is turned off while connecting the input jacks and speaker terminals. If you need to replace the power fuse, replace it only with a fuse identical to that suggested by this manual. Using a fuse of a different type or rating may result in damage to your audio system or your amplifier which is not covered by warranty . MOUNTING AMPLIFIER 1. [. . . ] If the protection LED still Comes on, then the amplifier is faulty and needs servicing . Check that the Input level control is set to match the signal level of the head unit. [. . . ]