you MUST have a 12v line to the battery and you MUST have a good earth to the cars Chassis

the question you asked made no sense :-
can the power lead be grounded to the floor? - that makes it sound like you want to run a 12V line through the cars floor therby giving you or anyone touching the car an electric shock?!

DO NOT run the 12v line and the Audio lines down the same side of the car - run them down opposite sides, this gets rid of the bussing alternator whine interfeerence that you'll get.