Subaru 1998 Forester Owner's Manual page 205

B Trailer lights
CAUTION
Direct splicing or other improper connection of trailer lights may
damage your vehicle's electrical system and cause a malfunction
of your vehicle's lighting system.
Connection of trailer lights to your vehicle's electrical system requires
modifications to the vehicle's lighting circuit to increase its capacity
and accommodate wiring changes. To ensure the trailer lights are
connected properly, please consult your SUBARU dealer. Check for
proper operation of the turn signals and the brake lights each time
you hitch up.
Starting and operating
HS0146
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