Might be unrelated to what this thread specifically addresses, but there is one more parameter to consider especially in the case of swapping gear ratio: the ratio adapter, that flat thing has a gear in it that "adapts" the counts or whatever units of measure to give a somewhat accurate speed reading. May be or not relevant...

 

If i'm interpreting the wiring diagrams correctly i'd concentrate on speedo first and you may end up fixing the cruise as a byproduct.

 

Until the speedo works there is no way you will get the cruise working.