Once in a while I find a loose wire at the terminal where the safety sensor and wall control attach to the garage door opener’s circuit board. You will find it located somewhere on the side of the motor head, possibly underneath one of the light covers.
Most older openers have screw down terminals. You simply wrap the stripped end of the wire around the post and gently tighten down the screw. Be sure to wrap your wire clockwise so that it doesn’t spin off when you turn the screw.
If you are working on a Home Run wiring configuration, you will end up with three wires that need to be twisted together before they are attached to the terminal. Linear and older LiftMaster, Chamberlain, and Craftsman openers have a “common” terminal that is shared by the safety sensors and the wall control wire (the middle one in the picture above). It may end up being too thick to fit. When you twist the three wires together, leave one of them about an inch longer than the others and wrap only that one wire around the terminal.
Newer openers have push terminals like you would find on a speaker. Gently depress the gate and slide the wire in. If your paired wires are too thick, you may need to splice in a thinner wire so it fits.
Be sure not to leave the wires in such a way that the bare ends could come in contact with each other. This will cause a short that leads to a safety sensor to malfunction, or in the case of the wall control wire, it could cause “phantom operation”.