Those are hard to come by, Dell does not publish them ,sometimes they get leaked.

 

Problem is they move the pin positions around from model to model sometimes.

 

This is the only 34 pin diagram I have ever found, no guarantee it is the same for yours.

 

http://www.lnmdesign.com/400sc/front_pnl.html#FNT_PNL

 

You can destroy the usb controller on the mobo. if they are connected wrong.