See
Figure 1. With the vehicle started and in neutral, press and hold the reverse switch in the left side controls until the reverse lamp illuminates.
FLHTCUTG: The lamp in the tachometer indicates that the reverse is enabled. See
Controls and Indicators → Instruments → Instruments: FLHTCUTG.
FLRT: The lamp in the speedometer indicates that the reverse is enabled. See
Controls and Indicators → Instruments → Instruments: FLRT. Release the reverse switch. The neutral lamp turns off when the reverse lamp turns on.