Wiring a voltage regulator for 2nd servo

[teamtom]

Could someone give me a clue as to how to solder in a MPI voltage regulator to run my rear servo on my clod. I'm running the front servo from the SR but wanted to just run the rear servo and not overload the BEC. The regulator looks like a servo extension cable with a black box in middle. I'm running hitec digitals and need to know which wires need to be spliced into the main power cables and which I need to keep connected to the rx pack. Also, what should I ground to what, keep the negative connected to the rx, put it into the battery main cables or what?

Thanks!
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