The backup light switch is located on the transaxle, screwed into the top of the transaxle casing, part number 4074. Having the ignition key in the on position, moving the gear shift lever backwards should trigger the back up light. Again if the lights do not come on the probable causes include the ignition switch, gauge fuse, bulbs, and wire harness. Consequently, if the light remains on continuously with no correlation to the shift lever's position excluding the reverse, check the wire harness. If only one light switch turns on the light, ensure that the bulb is good and the harness of that particular light. To check the back-up light switch, remove the electrical connector and un-screw the switch on the transaxle, then check with ohm meter if continuity is present only when the plunger is pushed inward and no continuity when the plunger is released. The switch and harness connector are on the side of the transaxle by the starter. If it the switch is defective then remove the electrical connector and the switch and remove it and replace it with a new one. To check the new switch, install it as a temporary switch and press the plunger with an ohmmeter connected across the switch terminals; continuity is attained only when the plunger is pressed. Last of all, screw the new switch tightly into place.