int l1=4;
int l2=3;
int saklar=2;
void setup() 
{
  pinMode(l1, OUTPUT);
  pinMode(l2, OUTPUT);
  pinMode(saklar,INPUT);
}

void loop() 
{

  if (digitalRead(saklar)==HIGH)
  {
    digitalWrite(l1, HIGH);
    delay(400);
    digitalWrite(l1, LOW);
    digitalWrite(l2, HIGH);
    delay(400);
    digitalWrite(l2, LOW);
  }
  else
    {
      digitalWrite(l1, LOW);
      digitalWrite(l2, LOW);
    }

}