Phone going nuts when using 3.5mm plug- Need schematic..

Very strange problem using my HTC One (2013 model) when using it with the stereo on my motorcycle...

The bike uses a standard 3.5mm input cable that plugs into the stereo's wiring harness. The problem is for some reason, the phone will think it is connected to a mic/button headset and will freak out skipping songs (Pandora) redialing the last number (dozens of times) or launch Google One- generally freaking the frack out until I unplug the cable.

I say for some reason but it is obvious the phone thinks it is connected to a headset with a button and the button is being pressed repeatedly and randomly. When I initially plug in the phone (and when I'm not having problems) it shows the normal headphone icon but during one of it's "seizures" it clearly indicates it thinks it has a headset connected.

I am at a disadvantage in that I don't know how the button press is signaled (no pinout or schematic) so I am unsure where to start. My initial thought would be a short somewhere but the 3.5mm plug is a standard "3-ring" plug. The audio cable actually plugs into a harness in the bike's sound system (3 wire plug) and the strange part is when the phone is having a "seizure", I have disconnected the cable from the harness (and subsequently the stereo) with no change- it continued to freak out. Unplug the cable from the phone and it stops...

Phone works perfectly with 3 other vehicles, several standard sets of headphones and a button/mic headset.

Any ideas??



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