After losing a tank or two of milk due to the bulk tank not cooling right, I bought a separate thermostat and wired red and green lightbulbs to it. Red goes on when the tank is hot or empty, and green comes on when the tank is cold. Power comes from another circuit, not from the tank circuits. I can see the lights from the kitchen window or from the road. Total cost of the project was less than $100, and I sleep better now with this reassurance that the milk is properly cooled.