D1307 RTC -> Getting in to the Control Register to turn on SQW/OUT

I can not seem to get this to work...maybe I am being an idiot but:

Datasheet -> DS1307 RTC IC datasheet

My code:

#include <Wire.h>

byte control_reg_addy = 7;
byte data_to_write_to_reg = B10010000;
byte dev_i2c_addy = 0x68;

void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
Wire.write(dev_i2c_addy);
Wire.write(control_reg_addy);
Wire.write(data_to_write_to_reg);

}

void loop() {
  // put your main code here, to run repeatedly:

}

The chip works, it does output the correct time and increments every second.
I want to turn on the output pin (IC pin 7) that toggles every second (optional...1Hz, ~4KHz, ~8KHz and 32.768Khz) by setting the bits in the control register (address = 7).

The device has an i2c address of 0x68.

I have a 330ohm resistor and a green LED on the output pin. Switched out the LED etc and also tested with a multi-meter.

Where am I going wrong?

EDIT: PS If I can use the Wire library to accomplish this rather than writing my own bit-bang code that would be great!