Honda FourTrax Rancher TRX420FE1 2019 Owner's Manual page 178

Brakes
Brake Light Switch Adjustment
Refer to Safety Precautions on page 101.
Rear Brake Only:
Check the operation of the rear brake light switch (1) at the right
side behind the engine from time to time. Adjustment is done by
turning the adjusting nut (2). 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)
(1)
(B)
(1) rear brake light switch (2) adjusting nut
168 Servicing Your Honda