MP3 /Aux power

[joe3407nomad]

Ok, I hooked up an auxiliary power source ( cigarette lighter), to the bike and attached it to the windshield very much like the one on gadget's page. Works fine, got power to it! Next I purchased a USB jack that sits into the ( cigarette lighter) and plugged my MP3 player to it, it doesn't work! there's a light that comes on when you seat the jack so it is getting power. I checked the USB wire and its fine, even used another wire still no good. The MP3 player is charged and works, but when I plug the USB wire into the MP3 player it shuts itself off, unplug it, it plays. The idea was to power the MP3 player while I was riding and not have to run it on batteries. The USB jack is labeled Input 12-24VDC
Output 5V/ 700MA
There's probably an easy explanation if you actually know what your doing, but...
Thanks, as usual for all your help.
PS I tried to explain this as well as possible so if I ommitted any obvious info let me know!