Keypad Pin Sorter
Most keypads today are matrix. Each button connects 2 specific pins with no single pin in common.
This circuit uses pins 11-18 to scan keypads with up to 8 pins, but can be easily expanded to more pins.
You can adapt the code for most any Arduino by just editing the pin access number array (scanPin) and the variable (pinCount).
After the program is loaded and running, pressing any button should disply the pair of pins that it connects to on the Serial Monitor.
Here is the Sketch.