Why does only one speaker work when I connect my iphone to my Hi Fi system?

I brought a brand new Hi Fi system today, tested in the shop with my iPhone connected and it worked fine, both speakers working.
I tried it when I got home and now only one speaker works when my iPhone is connected using the audio in cable. Both speakers work fine when a CD is playing, why is this happening?

The most obvious reason is a broken lead or a bad contact, this could be at either end of the audio lead. The cheapest thing to do is try another audio lead, if that doesn't work it's a bad socket connection. If headphones work with your phone then the problem is either in the audio lead or the hifi audio in socket. Let's hope it's just the audio lead.

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