I had to create new byte read/write functions for digital lines 0-7 because they are implemented very “differently” (and I don’t mean that in a good way) in the hardware for the Mega. If you’re interested in how I did this, check out the new version 2.12 Arduino sketch and the new mega_data_read and mega_data_write functions.
To use the HV Rescue Shield with the Arduino, first download the revised sketch here. Set the MEGA #define to 1 and compile/upload the sketch to your board. Make sure you have the Arduino Mega selected in the Arduino Board menu, or the sketch won’t compile.
The Mega has more pin headers than the Rescue Shield, so be sure to install the shield all the way to the left, as shown here: