To answer some of your questions I have attached some photos. You show exactly what you get. Yellow lens with 2 LEDs, black plastic base and hex bolt with nut and washer. The black wire is power and the white wire is ground. Grounding can be done with a hex bolt or with a separate attachment point on the frame. The internal electrical parts are completely covered in what appears to be clear epoxy. This should make it suitable for boat trailers if your power plug doesn't short to ground. It doesn't have a waterproof seal between the lens and the base, as there are holes at the top and bottom for water to enter (and exit). I haven't installed this yet, but it looks like the hardest part will be getting the old original non-LED light (with a rusty bolt) off the trailer. Hope that helps.
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