OK. Everything is wired up and mounted.

Polarity is correct: Grisa replied with the info.

Here's my setup:

E-Maxx
Airtronics MX3
Feigao 540-8L
Battery pack (red wire removed on BEC)
2x6 Pro-Match IB3800 matched packs

When I power it up (with the throttle on high), after 5 seconds I get continuous beeping. I assume that moving the switch to the yellow side of the switch turns it on (although, my common sense tells me that the switch is making contact in the other direction - I read on another forum that MGM controllers break a kill circuit to turn the controller on - ?). No matter how I try it, I still get the beeps. The rest of the system works fine, and I have tried it with and without the BEC, getting identical results. I have also tried powering it up in reverse, same thing.

What's the secret here?

Thanks!