I have Faria Tach not displaying hours

[tntitans21399]

I have a 2004 maxum 2400 se3 with 5.0 mpi engine. The tach gauge wasn't working. I used the diagnostic tach tach wire in front of engine to check gauge. It worked, rpm and hours displayed. I then took off the 3 wire connector on the coil and cleaned the connections and tighten the nuts on the gauge and the rpm work but doesn't display the hours. What would cause this? Or is this a sign the tach is partly broken?

 

[alldodge]

I have a 2004 maxum 2400 se3 with 5.0 mpi engine. The tach gauge wasn't working. I used the diagnostic tach tach wire in front of engine to check gauge. It worked, rpm and hours displayed. I then took off the 3 wire connector on the coil

Probably a bad connection but....
What is your serial number?