Starting to make progress, I found that by following instructions at
http://www.logjamelectronics.com/swixinstall3.html, I was able to get a voltage level of between 0 & 5V from the steering harness. If you plan on trying this, DONNOT CUT THE WIRE as per the instructions. The 22K resistor in the tuner module is too high a value to match the resistors in the steering wheel. The wire is already carring 0-5V which is perfect for the tuner, so just splice it.
Please be carefull not to trigger the airbag!.
Now to my next problem, configuring the ini file for the correct voltage levels. I tried the hijack 'stalk_debug=1' command tonight, but could not get that to work. But using the hijack 'show buttons' did allow me to see three of the six possible buttons when pressed.
Things are looking up!