318B Hour Meter Supply With Low Voltage & Flow

On our 318B excavator, the cat hour meter supply in the machine is experiencing low voltage @ 16v (I am assuming that is low) & when a test light is put on it, it will not light up & the Cat hour meter only records a fraction of the time actually spent when running the machine. Likely it should show 24v? When the meter is powered up on the bench with a 12v battery it counts up the hours correctly. Any idea where to look for the problem? Ser # on the machine is 3LR00468. Thanks

318B Hour Meter Supply With Low Voltage & Flow