Instead your pre wire is broken and you need to get it replaced.
Garage door sensors not staying aligned.
Sometimes the sensor may be beyond repair due to wear and tear and in such a case your best bet is to replace the garage door sensor with a new one.
When the safety sensor is not properly aligned or something is obstructing the light beam the garage door will fail to close.
Start by inspecting the wires that are going into both of the sensors.
The liftmaster garage door opener lights will flash for ten times.
On the chance that it still doesn t the problem could be the wiring.
Connect the white wire from the sensor to the white terminal of the garage door opener and then the black and white wire to the grey terminal.
Now point the safety sensors at each other.
Press the button that closes the garage door on the garage wall or on your remote.
If the sensors are working the garage door should immediately stop closing and return to the open position.
If you have a laser level you can use it instead of a string to align your garage door.
If the door still won t stay shut double check that the sensors are aligned with each other.
If they aren t gently bend them to restore a clear connection and secure a clean escape from your.
If the leds on both sensors glow it means they are not faulty.
Cycle the garage door through the opening and closing actions using the control on the garage wall or the remote unit from a vehicle.
If the door does not close completely without hesitation.
Proper height for a garage door sensor is 4 to 6 inches 10 2 to 15 2 cm.
Now that you have made sure there are no obstructions and that both sensors are aligned properly your garage door opener should work.