Taramps Automotive Digital Voltmeter And Sequencer Vts 5.1 Blue Led, Black All functions are accessed by pressing the FCN key, sequentially. The activation of mixers and/or audio processors should preferably be done at the S1 output for a correct sequential activation (when switching on, from S1 to S5 and when switching off, from S5 to S1), thus avoiding unwanted transients when switching on the amplifier (popularly known as "pop"). IMPORTANT: Outputs S1 to S5 are intended only for activating (REMOTE input) of the sound equipment. Voltage Check: With the VTS 5.1 without the remote signal it is possible to check the voltage of the batteries, press FCN and the voltage will be displayed and whenever you want to turn off the display press FCN again. Function SPL:Press FCN for about 10 seconds until ?SPL? and ?On? appear. This function increases the overvoltage protection (default = 16.5V) to about 19.5V. To deactivate this function, press FCN again for 10 seconds, until ?SPL?and ?OFF?appear on the display.