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I recently purchased this part to allow me to plug in varios audio devices[/size][/font]
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MP3 Adaptor Part Number 1426121[/size][/font][font=arial, sans-serif][size=3]
http://parts.jennings-ford.co.uk/product-info/MP3Adaptor[/size][/font]
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But now connected the audio is very tinny and quiet compared to the CD and Radio, and only appears to be coming through 2 speakers.[/size][/font]

[font="arial, sans-serif"][size="2"]The guy who fitted it says it because thats all you get with this connection but this doesn't seem right to me. And I can't find anyone who has complained about the quality of the audio from this adapter.[/size][/font]
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Could anyone inform me (or point me towards who can inform me) if this is behaving correctly of there is a fault, either with the fitting or the part.[/size][/font]
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Also found this fitting video that doesn't say there should be any problems.[/size][/font][font=arial, sans-serif][size=3]
http://www.youtube.com/watch?v=3n_VTX7sLHU[/size][/font]
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Thanks in advance[/size][/font]

I'd say that the socket you plug the 3.5 plug into is out of alignment.

As the socket is a two piece unit sometimes the contacts don't always line up properly with the 3.5 plug being pushed in.

I'd suggest you gain access to the back of the socket and while playing music via the aux, wiggle the socket pieces around.

Once you get a better sound quality wrap tape around it to try and lock the positions of the socket parts.

Thanks, this sounds like the problem as on further investigation the audio seems to be out of phase.

Indeed.
The aux sockets are pretty crappy.
I avoided that potential problem by buying a cable with a 3.5 plug on the end and running it out through the centre console near my lighter socket.