Car aux not working without 12 volts cigarette liter plugged in

2010 FORD KA
55,000 MILES • 1.2L • 4 CYL • 2WD • MANUAL
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INFORMEDHAWK
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A weird problem has recently developed on my KA.

When my phone is plugged into the aux without the charger the sound sounds incredibly strange, really quite and tinny. This corrects it self when the charger is plugged in (from the 12 volts). I have changed phone to see if this corrects the problem.

There is also a lot of whiny noise coming from the stereo in aux mode with higher revs, I have tried a inline aux ground loop, to no effect.

Interestingly if the plugged in phone charger touches any metal bodywork in the car the aux then works fine?

Is this a ground issue? Is there a way I can fix this? It very suddenly came on.
May 5, 2019 at 3:56 PM
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STRAILER
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I would start by checking fuse #3 and #5 the ground issue is strange. Can you please shoot a quick video with your phone so we can see what's going on? that would be great. You can upload it here with your response. Here is a guide to help you test the fuses:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Please run down this guide and report back.
May 6, 2019 at 4:30 PM