Honda Pioneer 1000 2017 Owner's Manual page 209

Refer to Safety Precautions on page 123.
Periodically check the operation of the brake light switch. It is
located near the brake fluid reservoir.
The brake light should turn on just before the brake works.
Adjustment is done by holding the switch body and turning the
adjusting nut. Turn the nut in direction (A) if the switch operates too
late, and in direction (B) if the switch operates too soon.
LEFT FRONT
brake light switch
B
A