What do you mean 'two copies of the black wire'? USB uses a voltage differential (3-wire) data bus cable with grounded shield to minimize interference from external sources. Your unexposed wires and unsoldered connections could be a source of noise.

The [macam FAQ][1] mentions lowering image format frame rate. Did you try this?

You may also find [this article][2] of interest, in that it describe a problem with the way Mac OSX hands out USB bandwidth to isochronous devices.

For monitoring performance of your USB ports, the [iStats Menu tool][3] offers a range of status statistics including bandwidth performance.


  [1]: http://webcam-osx.sourceforge.net/faqs.html
  [2]: http://www.ioxperts.com/FAQs/faq_webcamx.html#erratic_anchor
  [3]: http://www.tucows.com/preview/607624