Left return lane and right return lane are the lanes by the flippers that send the ball in front of the flippers.

Q relay is the alternating relay. If the left outside rollover light and right outside rollover light are not working or not turning on and off, check the following:

Q relay switches - make sure the switches are clean and adjusted properly
F relay switch - red/white wire and yellow/green wire - make sure the switch is clean and adjusted properly
Light sockets - confirm light sockets are making proper contact with light bulbs