Lionel 3469 Dump Car
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          Suggested Configuration

          ACC + ## + SET
          AUX1 + 5 + BRAKE + 2
          AUX2 + 5 + BRAKE + 2

This picture is an overview of the Dump Car installation.  The Mini Commander is located in the belly of the car.  AUX2 was chosen to trigger the dump action.   An additional 1uf / 50v ceramic capacitor is required to be attached across the solenoid coil for a snubber. 

The trucks were insulated from the car so the car becomes the antenna.  The antenna wire is soldered directly to the retaining plate and routed to the Mini Commander terminal.  The terminal is bent over  slightly to provide vertical clearance.
The trucks were modified by removing the shoe and replaced with 3rd rail collectors.  These are fairly common and available from several parts dealers.  Only one truck needs the collector added.  Since the truck is isolated from the car body, a wire was soldered to the truck frame, near the back of the truck after removal of a small  area of paint.
This is the detail of the truck mounting to the car body.   The washers are the same fiber/plastic  washers used on the couplers.  The sleeve was made from 0.25" plastic tubing, drilled out to 0.2" and sliced to a 0.04 in height.  The car body truck mounting hole was enlarged from 0.2" to 0.25" to allow clearance for the new sleeve.