Make FirstPersonCam follow car direction

Basically I am making a driving/racing game. I have a cockpit camera: the script below allows you to manually rotate the camera while driving. This is not what I want. Hopefully someone can help me so it rotates horizontily when I press "A" or "D" (Left or Right arrows as well).

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 #pragma strict
 
  var distance = 5.0;
  var xSpeed = 125.0;
  var ySpeed = 125.0;
  var rightclicked : boolean = false;
  
  private var x = 0.0;
  private var y = 0.0;
  
  @script AddComponentMenu("Camera-Control/Mouse Orbit")
  
  
  function Start () {
      var angles = transform.eulerAngles;
      x = angles.y;
      y = angles.x;
  }
  
  function Update (){
      if (Input.GetMouseButtonDown(1)){
          rightclicked = true;
          }
      if (Input.GetMouseButtonUp(1)){ 
          rightclicked = false;
      }
  }
  
  function LateUpdate () {
      if (rightclicked == true) {
            x += Input.GetAxis("Mouse X") * xSpeed * distance* 0.04;
            y += Input.GetAxis("Mouse Y") * ySpeed * distance* 0.04;
             var rotation = Quaternion.Euler(-y, x, 0);
             transform.rotation = rotation;
      }    
  }

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