The unclued lights are all words of a kind arranged into anagrams (all are confirmed in Chambers: one is a proper noun and one is hyphened). The clued light which suggests this activity must be highlighted in the completed grid.

Across

6 Bush I see decaying the wrong way (6, hyphened)
11 Money in Ghana, if travelling (7)
13 Mass and area for hill (4)
14 Maybe makes Roman litanies, as I composed (11)
15 Arouse footballer with one run (6)
17 Inventor overheard attractive woman (4)
20 Number reserve seaside resort (4)
25 Armadillo president gently turned over (4)
...