Honda FourTrax Foreman TRX500FM2 2018 Owner's Manual page 192

Brakes
Brakelight Switch Adjustment
Refer to Safety Precautions on page 115.
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 SIDE
(A)
(B)
(1) (2)
(1) rear brakelight switch (2) adjusting nut
182 Servicing Your Honda