Through the deck
I did mine through the deck. At the same time I did my mast light, I also did an anchor light, as well as a deck light (the deck light is part of a masthead/deck light combo). I ran 4 wires, 3 hot one shared ground, up the mast. I drilled a hole in the deck, and brought the wires up from below. I filled the hole (after running the wires through) with silicone sealant, and then installed a four wire connector I bought from West Marine. I've watched closely, and had no leaking to date (it's been about two years since I did it). However, I have noticed I have to keep the connectors sprayed with WD-40 after stepping the mast, or they tend to loose connectivity. I also noticed that there were holes in the bottom of the "foot" on my mast, where either from the factory, or from a previous owner, wires had been brought through the deck directly under the mast. The holes in the deck had been sealed by a previous owner, so I can't say for sure how well it all worked.
