Nope - bad move - You can damage the electrics. Anything you plug in can spike and blow stuff!!
Use a thick wire and lead it directly off the battery or off a formal spur if one is fitted ( boats like sunseekers have proper spurs fitted which you can directly wire stuff off of - cheaper boats usually not. )
Too thin a wire over too long a path will overheat - so get the wire fused to prevent a fire!