cigarette lighters not working

i have an '04 S 430. none of the cigarette lighters work. if you put a phone charger in the front one, the light on the charger lights up, but it won't charge the phone. when you push the lighters in, they don't stay or heat up. all 3 fuses are good. is there some kind of relay in that circuit? it surprised me that they are only 15a fuses, so i thought there's something else in the circuit.