Are we talking about just the speed correction adapter on the back of the spedo?
Forget about the two speed vacuum switch for now.
Remove the link rod and just switch the adapter while driving, and see if it works in both positions, high and low, "neutral" will be in between the two.
I am guessing that the link rod is not the right length, or something is out of adjustment, you should know for sure soon enough. If you do shift the adapter fully and it does not work in one position then there is probably something wrong with the adapter.
Grigg
