voltage on 2001 Tige

I recently purchased a 2001 Tige 21v and had a question. It came with a Faria Pilot gauge (temps, hours, voltage,etc) and the hour meter does not work. It appears that the gauge needs 13.6 volts to engage the hour meter, but the boat is only charging around 13.4 when underway (about 12.6-12.8 at idle.)has anybody else had this issue and what did you do to fix it. Would like to use this gauge with out adding another gauge elsewhere. Anyone have any tips of what might help solve this??