If you look at my picture, notice that the red wire was removed from the servo connector, this is how you remove the wire:


Then simply use a pin and insert it into the exposed female red wire you just removed, and plug that wire into the #2 cell of your balance port on the 4S battery... use your voltmeter to check that the #2 cell reads 8.4V, that is the hole you want to plug the red wire into, this will bypass the BEC.

Only do this if your Rx is rated to handle 8.4V otherwise you'll need to get a UBEC that I linked above.

What manufacture of radio system are you using?

This makes sense. Does it matter if it is a 6s battery? Still port two of the balance plug? Thanks!

Traxxas and HPI. Will be trying a Spektrum Tx/Rx soon, just to make 100% sure it's not the radio system. Spektrum Rx does look to have a port for an external battery, maybe I just go that route?

Solved. Thank you all for your input. I learned a lot through this process (now running external BECs on most of my cars). I'm embarrassed to say that the receiver harness on the ESC was transposed....the whole time. So basically I was frying Rxs because the idiot that sold me the ESC had the harness plugged in backward the whole time.

HUGE props to Castle for helping me figure this issue out...even when I bought it used. That's customer service!

Facepalm!

Next time, post a pic of your wiring to help others get more clues in helping solve the problem... never did get an answer from you on the voltage coming from your BEC, that would've shown the polarity was reversed at that point as well

Excellent news. Glad they were able to help you out. They are able support everything we've ever made. Even products we haven't sold for 10+ years, they are able to do diagnostics over the phone.

In engineering, we spent a while looking at that wire harness trying to make it as safe as possible just in case it was plugged in backwards. That's why some of the wires cross each other before going into the plug.