I just bought a stereo to put on my boat and I'm having some problems with the install. It seems easy enough, but??? I've done cars before and never had a problem is there a difference when doing a boat install? There only seems to be three wires that need connected there's a red wire that says (Accessory, connect to existing ignition circuit or switched 12 volt source.) a yellow wire that says (Connect to battery circuit or constant 12 volt source.) and a black wire that is the ground. I tried all different kind of combinations and can't get any power. Tried multiple grounding locations too. Am I missing something?