I recently picked up a Castle external BEC 2nd hand with no instructions. I wanted to use with with one of my MMP's, any info, pics on wiring would be greatly appeciated.

Solder castle bec's positive and negative wires to esc's battery connector. Then plug it into an open channel in the receiver.

Reciever plug from the ESC stays plugged in it's normal spot as well?

Yes but i forgot to mention that you need to disconnect the positive wire on the esc. I disconnected mine at the receiver end.

Ok, thanks for the info!

i hope you have a castle link to programe it as you need to set the volts to what you want to run it at as stock volt is 5 volts