On my "new" to me 2007 FD GS20 OB there is a combo fuel and voltmeter gauge. The voltmeter works, but the fuel does not. Needle registers E. I know it could be the gauge, the sender, a connection, or a fuse, but I don't know how to figure out which it is. How do I diagnose the problem? For that matter I do not know where the fuel tank is on this boat. Obviously I know where to put the fuel in, but not where the tank and sender are? Thanks for any help or advice.