Wireless pioneer has stuff erected on island (7)
I believe the answer is:
marconi
'wireless pioneer' is the definition.
(I've seen this before)
'stuff erected on island' is the wordplay.
'stuff' becomes 'cram' (synonyms).
'erected' says the letters should be written backwards (in a down clue, letters go up).
'island' becomes 'i' (geographical abbreviation).
'cram' backwards is 'marc'.
'marc'+'on'+'i'='MARCONI'
'has' is the link.
(Other definitions for marconi that I've seen before include "The father of radio" , "Wireless inventor from Minorca" , "Guglielmo --, inventor" , "Italian electrical engineer, d. 1937" , "Italian scientist" .)