CC-688 T-Box siren output has built-in 10A relay. The factory default is generally high voltage positive output, and some customers require low voltage negative output, T-Box can directly drive the original car horn (general original car horn needs low voltage negative output), some model car's original horn cannot be driven after the engine off, These cars can install an alarm horn. Before installation, please confirm the T-Box siren output is positive and negative according to need. If the T-Box siren output is not right, open the case, change the PCB connection with soldering can change the siren output between positive and negative: