Honda Civic "overheating" and starting problems?

I think my car has 2 problems: 1)FALSE OVERHEATING READING - the engine is actually is not overheating and the thermostat has been replaced. What and where can I find the sensor that actually sends electrical signal to computer to raise or lower the gauge? 2) STARTER KEEPS ON BREAKING AND/OR BATTERY KEEPS ON DYING - starter has been replaced 3 times, battery is only 3 months (been checked and confirmed ok), and ignition switch is confirmed ok. Is there a voltage regulator circuit that regulates the voltage coming from alternator and tells the battery when to stop and start sucking current? Where can I find it?