Clio 3 rear parking sensors

Hello everyone.
I am in the middle of installing rear parking sensors in my 2009 clio and I've encountered some problem. To properly install the sensors I need to connect three wires: ground, backup light and +12acc. I have problem with the third one. Do you know where I can find a wire where +12v appears after I turn my key to the ignition postion? I've tried with a radio but there are only ground and constant 12v.