The schematic shows that the Right Target switch and Left Rollover button should turn on the X Selection relay unless O is already selected. Similarly the Left Target switch and Right Rollover button should turn on the O Selection relay unless X is already selected. There is some kind of Target Adjustment, probably made through a jones plug somewhere, but I'm not sure what that does. Anyone know?
Egg Head Selection relays (resized).jpg
Once X or O is selected one of the lights at the bottom of the playfield should turn on to show your selection. The selection stays on until one of the unused pop bumpers is hit. When that happens the pop bumper should be assigned the selection and the selection light at the bottom of the playfield should go out. Then the game is ready for the next selection.

/Mark