How to check if the machine(SWM-8802 Car Radio) is normal ?

Twisting the yellow and red wires together and connect them to the positive electrode of the power supply. Twisting the two black wires together to connect the negative electrode. Then insert the machine and then press the power button. After the boot is normal, connect the horn speaker cable. Connect two wires of same color to one horn and plug in the horn speaker cable to test whether the sound is normal.