You ask a good question. I just ran the software and rightly or wrongly assumed that wire.h would be manipulating the data on the only two SDA and SCL pins on the mega. Is there a step I missed?
On the 5883L board, the pins are labeled with SDA and SCL.
I've ordered an Adafruit 5883 based compass module, as it has circuitry to make it safe with 5v logic legals. Hoping this will work with the mega 2560 and it's on board pull up resistors tied to 5v. Maybe I wrecked the previous 5883 compass hooking it up to my mega??? Another mega on order as well, just in case.