Clarion XMD3 "boat horn work" Questions

...at all. horn not working. can't lock doors with key, Neither Speedometre is at 0 and milage isn't going up and now the boat is locked and we can't open it as the central locking is gone! Any

...boat electronics I noticed my stereo was dead. Just by chance I blew the horn and the stereo came on? Bad connection was my first guess. I have check all connection points hot & ground and they are ...