He needs a jump start and a replacement spare (6)
I believe the answer is:
jasper
'he' is the definition.
'a jump start and a replacement spare' is the wordplay.
'start' says to take the initial letters.
'and' says to put letters next to each other.
'a replacement' indicates an anagram.
The initial letter of 'jump' is 'j'.
'spare' anagrammed gives 'asper'.
'j'+'asper'='JASPER'
'needs' is the link.
(Other definitions for jasper that I've seen before include "stone used by jewellers" , "Opaque quartz" , "A man" , "Opaque reddish-brown semi-precious stone" , "Reddish-brown stone used in jewellery" .)