Car radios use to take a lot of current to run. Today, you can get by easily with just a power supply that will put out 2 to 3 amps of current at 12 volts. It does not have to be elaborate and can be made from a 3 amp, 12 volt transformer, a rectifier chip rated at 5 to 10 amps to convert AC to DC and a 25 volt/ 250 microfarad (250mf) capacitor to filter the DC. Connect an on/off switch in series with one leg of the AC side of the transformer. Run the other side of the switch to the white wire of a wall outlet cord. If the cord is a simple one with two brown wires just connect one of the brown wires to the switch. AC has no polarity. Connect the black wire to one side of a 2 amp fuse and connect the other side of the fuse to the other leg of the AC side of the transformer. You can now carefully plug in the cord to a wall outlet and turn on the switch. DO NOT TOUCH ANY WIRES OR METAL PARTS WHEN PLUGGED INTO THE WALL. You could receive a 120 volt AC shock that could kill. Measure the other side of the transformer from one leg to the other with a multimeter set to the maximum AC VOLTS range. It should measure 12 volts AC. If you get a higher reading then unplug the wall outlet, remove the transformer completely and turn it around. Reconnect and repeat the above steps to read the AC voltage on the other side. It should now read 12 volts AC. Turn off the switch, unplug the circuit and start building the DC part of the circuit. Connect both sides of the transformer to the middle two connectors of the rectifier chip. Connect the plus side of the 250mf capacitor to the + leg of the rectifier. Connect the minus side of the 250 mf capacitor to the -- leg of the rectifier. Run a red wire to a post or the plug of the radio from the + side of the 250mf capacitor. Run a black wire from the --side of the capacitor to a post or the plug of the radio. If your plug has a green wire connect it to the base of the transformer and to the metal chassis of the radio. BE SURE TO OBSERVE POLARITY WHEN CONNECTING THE RADIO. Plug into a wall outlet, turn on the switch and set the multimeter to read 25 volts DC. Connect the positive side of the multimeter to the red post and the negative side to the black post. You should read 12 volts DC on the meter. If everything looks good, turn off the circuit and unplug from the wall. Build a wire screen cage around the power supply or enclose it in a wooden box so nobody can touch any metal parts. Finally connect the SPEAKERS to the car radio, and connect your newly built power supply to the power outlet of the radio. Enjoy your creation.