I have a garage door opener that was manufactured in 1996. It only has 3 screws to connect the control wires. I am sure 2 are for the manual opener. My question is where and how do you connect the 4 wires that come from the safety eyes located at the bottom of the door on each side. The screws are labeled 1,2 and 3. Is there another screw for a ground or am I missing something.