I agree that there is evidence of low voltage. I would look at high resistance in the circuit--often due to corrosion--and often forgotten in the ground circuit.
Another possibility is excessive draw on the water pump circuit.
Do you have a digital volt meter aboard? (all of our cruising boats should)--check the voltage when you are running the water pump. (I have the Link 10 system hooked directly to the battery, which is how you should have a battery monitor system. But with down stream issues, measuring the voltage at the console is more important.)
Another possibility is excessive draw on the water pump circuit.
Do you have a digital volt meter aboard? (all of our cruising boats should)--check the voltage when you are running the water pump. (I have the Link 10 system hooked directly to the battery, which is how you should have a battery monitor system. But with down stream issues, measuring the voltage at the console is more important.)