If your garage door won’t close there is about a 90% chance it is because of a problem with the safety eyes. Most of the time it is simply alignment or obstruction. But, I do see a fair amount of broken wiring and/or bad splice connections. And, sometimes they just go bad for no reason whatsoever.
This page will explain how to figure out what is going on with your garage door opener safety eyes, as each brand has its own quirks and flaws. Nearly every safety eye related service call I go on could have been resolved by the homeowner if they knew how to approach it. If your door is having problems closing, this page could save you at least an $80 service charge.
LiftMaster, Chamberlain, Sears-Craftsman Safety Eyes
The most common safety eye out there is the one I get the most service calls on, and for good reason–it is a stupid design.
The brackets that hold the eyes are made to clip onto the track, but they come loose frequently. Also, they are not easy to mount in situations where there is a concrete wall or other obstruction right up against the track. They can be mounted into the concrete with smash anchors if needed.
Besides being difficult to install, these safety eyes are a pain in the neck to line up. The sending eye is sort of an orange/amber color and it will always be on if there is power. The receiving eye will light up SOLID green if it is making a good connection. However, if the connection is not very good, the green light can flicker, but just a tiny bit and it is hard to see. It is common for people to think that the green light is on when it is actually flickering, in which case the door may close, but it may also reverse.
Luckily there is a way to tell if the safety eyes really are the problem: if the light on the motor flashes about ten times after the door reverses to the open position, the eyes are the source of the problem. It is usually just a matter of alignment.
To align the eyes, start by making sure that the bracket is tightly clipped to the track or otherwise mounted nice and solid. Loose the wingnut on the sending (orange) eye, and aim it straight across at the receiving eye. Tighten the wingnut. Now, go to the receiving eye, loosen the wingnut, and adjust your aim until the green light comes on nice and solid. You should be able to wiggle it side to side and up and down while maintaining a bright green light.