To run 12v dc things in a car the battery outputs 12v regularly but it can go as high as 14.4 when the engine is running I need a circuit to regulate this at say 12v 10 amps to prevent over voltage?

the alternator is what puts out the 14.4 volts. if you wish to figure out the circuit use the formula A*R=V so you take the voltage 12 divide by the amp 12 and you get 1.2 as the resistance. so in your circuit, the max allowable load is 1.2 ohms.