speakers only playing from one side of the car

I recently bought a new stereo, but when i listen to music off my phone through an aux lead the sound only comes out of the speakers on the left side of the car not the right, but when i am listening to a CD or to the radio all of the speakers work fine. I was wondering if it was something to do with the stereo or the leads

it's the leads, you need one with tip, ring and sleeve (stereo) you got the mono version