(NORTHSTAR) GPS & Sounder Lock MARINE SOUNDER & GPS LOCK Instructions: (a) Remove one factory
knob from either side of unit. (b) Turn key clockwise and remove from
lock. (c) Screw GPS/Sounder lock into female thread until tight. (d)
Insert key and turn counter clockwise. (e) Knob will spin freely when locked
correctly making it impossible to remove.. Note:
Lubricate often and record key number for replacement keys when
lost.