Bones, I believe it is the difference between 'Water Resistant' - and 'Immersible' that is the issue - automobile hydraulic brake cylinders are not really 'immersible' either - they just better tolerate the exposure- when cool. Electric solenoid - not so good submerged ;>) Don't forget to disconnect the trailer lights when launching - some of us have electronic control units for the trailer lights - this can get expensive at worst, and annoying at best,trying to find the 5A fuse inline (toyota) when dunking the lights! Take Care,Have Fun,Go Sailing GO