How to find car horn cable

The specific steps are as follows: 

1.Black is generally the power supply part, usually 5, respectively, ask B+, ACC, ground wire, antenna power supply, small light wire;

2. Brown is the horn wire, generally connect the horn up and down, do not cross, otherwise it will Burn out the audio amplifier, generally, front left, front right, rear left, rear right; you can use the multimeter to distinguish between the ohm range, and there will be a squeaking sound when the power is turned on immediately,...