I chose to make this Instructable as I was unable to find a device similar to this available for purchase
A Video of it in action is attached as it takes too long to convert. You probably need Quicktime or VLC.
The controller uses a 12V SLA battery and a transistor to control when the lights should be active by monitoring the speaker output. It works best when wired to a subwoofer as it only activates the lights when a beat is present.
You will need:
A box to put it in (I used an old Pioneer home theater speaker)
A Heavy Duty Transistor( The transistor I used was a ST W14NC50 from an old Compaq power supply unit)
A soldering iron
A switch (optional)
3 Speaker input ports(don't know what their actually called)
A 12 Battery. (Make sure the voltage isn't to high over 12V as you may blow the LED's)
Step 1: Constructing and soldering the circuit
Step 2: Test the circuit.
To test the circuit find a battery with a 12v charge. Connect it to the red and black wires. Connect the two orange or amplifier wires to a smaller battery such as a 3V computer battery. If all goes well the LED's will light up. If not, try reversing the polarity of the 12V LED strips or testing them with the battery itself.
Step 3: Making it look nice.
In order to make it look neater and to easily mount it within a car you should mount it within a box. I used an old speaker as it already had a port that could be used to wire the LED's into. Any small box should do though.