I am setting up my Texas Warbirds P51 and it came with these excellent CY Models electric retracts.  IF anyone has had to deal with Robart before, these CY models e-retracts feel and function, so far, much better than Robart E-retracts.  Some important points to make about setting it up.  You need to use 7.4 volts to 8.4 volts. The red electronic retract control unit has two leads. One gets plugged into the receiver for the radios' gear channel. The other gets plugged into a battery source of 7.4 to 8.4 volts.  When you 1st connect the system and power on the radio, the lights on the red retract control unit may not turn on and there may not be any reaction when you toggle the gear switch on the radio, this does not mean it is defective or not working.  This happened to me.  What you have to do, is go into the transmitter radio and program the gear switch in several different ways.  First, use a 2 position switch and program the switch so that the travel goes from center to the right with the switch in one position and then it goes the other way when you flip it.  this is the algorithm that will help trigger the retracts to work.  Once you get this done, then program your radio so that the pre-flight switch position is checked and prevents the retracts from going up when you power the radio if by accident the switch was flipped in up position.  Finally, i was able to connect the power lead from the red retract control unit into an empty slot on my central box receiver unit, and it works, that way, I do not need a 3rd battery.