My '89 Ski Nautique (Ford 351) overheated due to impeller failure in the external water pump. I replaced the impeller and the boat runs great. But the temp gauge continued to show overheating (in error). I replaced the temp gauge and thermostat (both, now twice) as well as the sensor on the engine block -- but the new gauge still doesn't work. Occasionally, the red light comes on, but I know she's running fine. Appreciate any ideas?