Linked ad groups will be shown in the Rule Editor
To link ad groups:
Linked ad groups that are selected within a rule as a source, target, or negation ad group cannot be removed. To remove, first unselect the ad group from any rules, or delete rules the ad group is used within.
By default, only enabled ad groups and campaigns are shown. Use the switches for "Show Archived Campaigns", "Show Paused Campaigns", "Show Archived Ad Groups", and "Show Paused Ad Groups" to adjust the view.