Opel MOVANO Owner's Manual page 280

IMPORTANT
253) The ABS with which the vehicle may
be equipped will not control the braking
system of the trailer. Particular caution is
required on slippery roads.
254) Never modify the braking system
of the vehicle to control the trailer brake.
The trailer braking system must be fully
independent from the hydraulic system of
the vehicle.
255) After fitting, screw holes must be
sealed to prevent exhaust gas infiltrations.
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