I have been working on making a pinout for the front panel connection board that comes in the PowerMac G5 cases.
I have NOT verified this by actually hooking anything up. I have only pinned it out with a multi-meter and used the standards for USB, Firewire and Audio to assign the actually pins to something meaningful.
I am unsure of the LED and Power Switch because something just does not seem right with what I have found out. I am thinking it might be safer to wire up the LED and Switch seperate from J1. Firewire power is at 30V and that seems like a lot for a LED.
Again, use this at your own risk. I take no responsibility for any damage that might incur.
EDIT: I have converted this to a PDF and changed my numbering to match what Neo used. Also included in the PDF drawings for USB and FireWire connectors.
