Trying to drop 13.5 volts to 10 volts in a car
If you want '10v' then you need a regulator, a resistor/capacitor will not do. 

However, you may not need 10v. If it's a signal to a car component, then the nominal 12v 'car voltage' will probably be accepted. Read the data sheet very carefully, or post a link to it so we can.