Quoted from SealClubber:Have to look in the manual for Switch #23 to find the location. Probably in the u-turn loop behind the center drop targets.
Press it down with your finger to make sure it is working. If so it just needs to be adjusted.
Make sure the wire part of the switch is not sticking against the playfield.
Roll a ball over the switch to ensure the ball will activate the switch. If not, GENTLY bend the wire up until the ball activates the switch.
Had my manual handy. Switch 23 is on the upper playfield, toward the top right corner of the machine. It's the exit switch for the loop.