Lotsa info to share. I now have the horse car/corral, cattle car/corral working very well. Rob suggested two switches for the horse car and corral, but I elected to go with a double pole/single throw toggle to operate both units together. The problem is that, at least in my case, the car requires twelve volts to operate. At that voltage level the horses will literally fly off of the corral track. The corral works best on 5 volts, supplied from a variable voltage tap to one pole on the switch and 12 volts from a different source thru the other pole to the OTC track connector for the car.
Also, I found a segment in Jim Barret's repair tape #4 which was of some help, but did not address the subject of varied power requirements at all. He also failed to mention that there is an adjustment screw to control the intensity of the track vibration in the car. Remove the body by removing one small screw in each end of the car and "carefully tipping the ramps out just enough to allow the body to lift off. An L shaped bracket rests on top of the solenoid magnet which vibrates the track and lowers the ramps. This bracket runs down the back of the solenoid and is attached to the track by a single screw in a slot in the track. The screw is accessed by removing the flat spring with a curved end which is moved by opening and closing the rear door on the car to position the spring to block passage of the horses or allow the horses to pass thru the car. Once the screw is loosened, the track can be pried upward to produce greater vibration to speed up the horses or pressed downward to damp vibration and slow the horses. Tighten the screw while holding the track in the desired position. Try the car and re adjust the screw as needed for desired performance. Replace the flat spring so that the two ply section spreads over the car edge and secures the length of the spring. There are two vertical tabs projecting upward from the flat spring .To replace the body, Look inside at the door on the flat spring side. A tab projects out from the door. Slide the door to a place where the door tab will slide down between the flat spring tabs when the body is replaced on the car, being careful again to tip the ramps out just a bit when the body is placed on the car. Replace the 2 end screws and try it out.
Actually, there is a whole other topic associated with how to control the movement of the livestock thru the corral. For that process, consult the Jim Barret
volume 4 article or post another question and I will write another looooong drawn out explanation.
Hope this is helpful to someone!