There is a hand-held remote that goes with the car, K-712RC. You would switch one and only one of the A, B, or C up, and then one and only one of the 1 thru 8 up on the car, to set its address. Then on the remove you had to press one of A, B,C, then 1 thru 8, to activate the car. This part I am pretty sure on.
Now the parts I am not sure on. Supposedly the remote did not pass FCC, so when Lionel took over some K-Line manufacturing, a new remote and new electronics in the cars, and there was no forward or backwards compatibility. Then somehow it moved on to Williams.
The original remote on the K-Line website:
K-Line K-712RC
The K-Line Amtrak dump car:
K-Line K712-1031
The K-Line by Lionel remote:
K-Line by Lionel remote
(can't find a K-Line by Lionel remote dump car at the moment).
The Williams remote:
Williams remote
Wiliams remote control cars (based on K-Line)
Williams remote cars
and as you can see, at least K-line and Williams has a orange Amtrak remote dump car, and you would need to know which one you have. Confused? It gets worse.
I have a bunch of the original K712* and K713* cars, and about half of them would not work with the remote out of the box.
The cars could also be activated by a remote control track, of which many companies make, but its more fun to able to dump the car anywhere on the layout.
The red button is a reset, if the bucket got stuck in the up position (say the power got cut before it could go down), you could reset it then (when the power is back on). It is not like a Lionel postwar with its stabbing electromagnet, the K-Line uses a small motor to go thru the motion.