Disconnect one of the retracts from the receiver and plug it into the load side of you volt meter and the plug the other side (power or batt) of the volt meter into the receiver retract channel. What you want to do is put the meter between the retract and the receiver. Now check the voltage drop and amperes being drawn as the one servo deploys and retracts. Then do the same for the other retract. Then, with both retracts plugged back into the receiver, connect your meter between your battery and your switch and deploy and retract both units and note the amperes used. Are your retracts bottoming out? Do they go into the over-current protection mode? you can tell because they produce a whine before they shut down also, your amps will spike and the voltage will momentarily drop.