need help with 1 master arduino and 2 slave for car wiring harness

Using Arduino Networking, Protocols, and Devices
4

hi,

i dono how far i can help u....... but i have a simple serial communication programs between two arduino's. i hope it will help u. u can easily modify for ur use.

Master sketch

int i;
char reader[10];

void setup()
{
pinMode(13,OUTPUT);
Serial.begin(9600);
Serial.print("2OFF");

}

void loop()
{
  
  if(Serial.available()>1){
  for(i=0;i<10;i++){
    reader[i]=Serial.read();
    delay(2);
  }
}

Serial.print("2ON");
delay(500);
Serial.print("2OFF");
delay(5000);

for(i=0;i<10;i++)
reader[i]=0;
}

Slave sketch

int i;
char reader[10];

void setup()
{
pinMode(13,OUTPUT);
Serial.begin(9600);
}

void loop()
{

  if(Serial.available()>1)
  {
    for(i=0;i<10;i++)
    {
      reader[i]=Serial.read();
      delay(2);
    }
  }

if(reader[0]=='2'&&reader[1]=='O'&&reader[2]=='N')
digitalWrite(13,HIGH);


else if(reader[0]=='2'&&reader[1]=='O'&&reader[2]=='F'&&reader[3]=='F')
digitalWrite(13,LOW);



for(i=0;i<10;i++)
reader[i]=0;
}

for more detail see this video - YouTube