I-phone play

[53driver]

Does the 1/8" plug insert fully into your phone? Sometimes a case will prevent that.
If you're not sure, try moving the balance to either side on the iPhone or the B and see if you have signal.
Try another audio source with 1/8" output to see if you can eliminate the phone or the AUX input.
If the AUX input always sounds bad it could be that 2 of the 3 wires that connect to the factory wiring harness have been reversed which would lead to your L/R being out of phase.

I keep forgetting to advise people to check for this! Well done, MisterB!
Hopefully that solves the issue!
Cheers,
Steve