I have a 2000 Fleetwood Discovery with a 275 cummins diesel engine and just had my alternator rebuilt.  I am new to this and my question is should the wire connecting the alternator to the starter start out as a 10 gauge wire and reduce to a 6 gauge wire?  I am only getting 13 amps after having the alternator rebuilt.  The voltage gauge reads not quite half way in the normal range when the engine is started.  When I start the generator, while the engine is running (new batteries), the voltage gauge drops to approximately one quarter of the normal range. The generator is a 7500 Onan diesel.  Is this what the readings should be?