This is intended for micro-crawlers instead of models with hairy ass servos. Just because you can do something is not the same as should do something - capice?
This is made for power the steering servo independently of the BEC by connecting to the 3S or 4S propulsion pack through the JST-XH connector. HOWEVER, the servo only gets 7.4V (2S, in other words) while the BEC keeps feeding the radio something less, often 6V while at the same time, the propulsion motors gets the full jolt. Easy peasy!
Nice thing of going straight to the analog-source for the servo instead of interposing a BEC to create low quality synthetic digital-current, is your servo performs better without the risk of going poof if you try feeding it 3S or 4S directly. The downside is ripple, which with a big motor system is trouble but for a micro crawler is usually OK. Word to the wise, the ripple is why we do not recommend using this is larger class servos like DS505 and up, capisce? Don't be stupid thinking you know better than us.
Here's the thing, a lot of microrigs use a 3S packs but their BEC is sized for a stock servo producing 1/3 the output of one of our DS105CLHV or DS125CLHV sub-micro servos. Basically, the factory BEC simply don't have the stones to deliver enough current. So folks wonder, 'Can I connect my servo to 3S used for propulsion?', and the short answer is, nope because the servo will go poof and emit the magic smoke.
So instead of interposing a BEC to create current by going from DC to AC and back to DC (a digital process), this harness adapter lets you tap directly into a propulsion pack to steal 2S for the servo. This gives the servo genuine analog current (as created through chemistry, e.g. the battery) versus synthetic. You feed the servo the real thing!
Instantly, the servo gets more and better quality juice to run on. The power is of much better quality power because it's not synthetic (the BECs make 2S digitally using FETs while batteries basically use chemistry to create a smooth more analog voltage and current).
Everything has a downside, and the downside of tapping into the propulsion pack to power the servo, is this consumes the propulsion pack's life that you'd otherwise use to run the rig. Of course, the BEC does exactly the same thing (but with even reduced run time because it's not 100% efficient). So both using a BEC and tapping in directly reduce run time, but with the BEC this practice reduces it a bit more.
However, there's an alternative which is to run a dedicate pack (yes, just for the servo). For this you need either an HV2SV-X or HV2SV-D (plus a pack). We offer dedicated control electronic packs in various capacities ranging from 850mAh through 5000mAh - but - for the tiny rigs even these packs are physically too large making this harness the best alternative.