Trouble with RC car Hack

i followed instructable on using arduino replace control chip , send logic signals through cars circut board program cars movements, beleive follwed , seems work except turning left. turns right fine. when program says turn left goes straight. rx2 chip means gnd pin 2 , right, left, forward , reverse pin 6, 7, 11, 12 on chip. if helps troubleshooting i've tried swith pins in arduino, weirdly still turned right before, if take 1 wire out doesnt work @ all. code:
 car test.

pluged wires arduino pins
*/
int forward = 12;    // forward pin
int reverse = 11;    // reverse pin
int left = 10;       // left pin
int right = 9;       // right pin

// setup() method runs once, when sketch starts

void setup()   {                
 // initialize digital pins outputs:
 pinmode(forward, output);
 pinmode(reverse, output);
 pinmode(left, output);
 pinmode(right, output);
}

void go_forward()
{
 digitalwrite(forward,high);   // turn forward motor on
 digitalwrite(reverse,low);    // turn revers motor off
}

void go_reverse()
{
 digitalwrite(reverse,high);    // turn reverse motor on
 digitalwrite(forward,low);    // turn forward notor off
}

void stop_car()
{
 digitalwrite(reverse,low);     // turn revers motor off
 digitalwrite(forward,low);    // turn forward motor off
 digitalwrite(left,low);
 digitalwrite(right,low);
}

void go_left()
{
 digitalwrite(left,high);     // turn left motor on
 digitalwrite(right,low);     // turn right motor off
}

void go_right()
{
 digitalwrite(right,high);    // turn right motor on
 digitalwrite(left,low);      // tune left motor off
}

// loop() method runs on , on again,
// long arduino has power

void loop()
{

 go_right();
 delay(1000);
 go_left();
 delay(1000);
 go_right();
 delay(1000);
}

sounds wiring problem me, if swap wires , same thing.

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