Honda TRX500FA6 AT Owner's Manual page 201

Brakes
Brakelight Switch Adjustment
Refer to Safety Precautions on page 125.
Rear Brake Only:
Check the operation of the rear brakelight switch (1) at the right side
behind the engine from time to time. Adjustment is done by turning
the adjusting nut (2). Hold the rear brakelight switch and turn the
nut in direction (A) if the switch operates too late and in direction (B)
if the switch operates too soon.
RIGHT REAR
(A)
(2)
(B)
(1)
(1) rear brakelight switch (2) adjusting nut
Servicing Your Honda 191