Mgm 16018
 

I have the new MGM 16018 with the built in bec, Do I plug the speed control into the second slot on the receiver, or into the Bec slot

You plug in the second slot on the receiver. The red wire in the ESC connector sends power to the rest of the electronics.

Yeah the pins where the Red and Black wires plug in to the reciever are all connected in parallel with their respective color. You could plug the controller into any of the slots* but it would be on the wrong channel if you didn't use the second.

*With the exception being the BEC slot because it doesn't output a signal.