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Fairly simple question: Do redstone dust/redstone torches/switches/etc. work underwater?
Nope, you can't place them on tiles with water, they pop back up. If you have placed them already and water flows over them then they will do the same.
Here's a picture of me trying to place a redstone torch down, while a sheep looks on in bewilderment:
Yes, if you make a tunnel. Here's some images of me doing just this:
Well... Sticky piston plus Redstone blocks. Expensive, but no tunnels needed.
Redstone can't be placed underwater without a mod. Check out the mod forum or Minecraft Mod Center.