Wow, I can't believe they gave up....they are the experts, they should just order the entire assembly strip out the old and add in the new, aparently they are not finding an electiical malfunction in the system and that is understandable as they are mechanicaltechnicians and not electronics techs, we would come up against this sort of situation from time to time in our dealership as we couldn't bench test the computer in a complete way, so we would send it all back to the factory and we would get a replacement assembly for it, this however was not related to a cruise control problem but rather a no start condition on early GM's.I have before me a phone # and web page for a company that makes sells and has all the installation directions easy to read and easy to follow for Harley cruise replacements.
I feel your pain man, this is one condition that no one is going to come up with the solution over the wires, and as you can see even hands on as a defeat!!
Well here goes and i hope these folks can help your situation out.
http://www.cruisemount.com/installation.html is the web page and here is the phone#: 1-620-279-4253.
As we speak I have put a call through to them in regards to your situation please provide me with all the pertinent information on this bike and what they are saying is or isn't happening when the cruise is pushed on.
Thanks