a higher ranking keyword prevents ad from running in Adwords
Re: a higher ranking keyword prevents ad from running in Adwords
Assuming these keywords are in different Ad Groups, you would want to add the lower ranking keyword (as Exact Match) as a negative keyword in the Ad Group that has the higher ranking keyword you are trying to avoid triggering. That will prevent the ads in that Ad Group from serving those searches.
I would caution you that this does not guarantee that the lower ranking keyword will serve the traffic instead. It just blocks the higher ranking keyword from serving the traffic.
In order to get the lower ranking keyword to serve the traffic, you may need to experiment with different ad text in that Ad Group, or try changing the bid on that keyword.
Hope that helps!
Google AdWords Top Contributor