Recall that the serial data at the ECM is 5V (TTL), don't go anywhere near 12V or it will pop the port on the micro-controllers.

D10 is RX to the EBL ECM
D11 is TX from the EBL ECM
D12 is ground

For the most part TX is always active (ECM powered up). RX is active when flashing and when a bank selection is made.

RBob.