Also, the earth for the 20 relay comes via either of the 10's card reels when they are at 2nd position. Earth is fed to them via a switch on the ball index relay (which is active when a ball is in play) and then via the make/break switch on the player relay. Also, when the 20 relay is activated , earth is seperately  fed to the 1st position on the 10's card reels (not sure why).