Without the pinouts of the sockets (of the respective machines) you're pretty much shooting in the dark.

A Bluetooth device will show on the "USB" device tree in System Profiler. (It shows as "Bluetooth USB Host Controller" on my Macbook Pro, I suppose I could check what the stock Bluetooth looks like on a G4 Powerbook as well.) If it's electrically active at all it should show up on that tree, even if it's not recognized as anything. (For instance, a silly USB missile launcher with no Mac driver shows as a "Composite Device" when plugged in.)