dont know about the alternator (scared me the other day though i drove through about a 18" of standing water and the lights started to dim... but all is well now) but i put together an outdoor stereo and waterproofed all the wiring using liquid electrical tape i found at home depot... works beautifully, just paints on and dries water tight if you do it right, itd be great for waterproofing those plugs... it also peels right off with a little effort and an xacto in case you need to repair/replace something