New cracks in the lead -- pull and disconnect! (6)
I believe the answer is:
unplug
'disconnect' is the definition.
(synonyms)
'new cracks in the lead pull' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'cracks' indicates putting letters inside (some letters create an opening in the word).
'in the lead' becomes 'up' (similar in meaning).
'pull' becomes 'lug' (I've seen this before).
'n' put within 'up' is 'unp'.
'unp'+'lug'='UNPLUG'
'and' acts as a link.
(Other definitions for unplug that I've seen before include "Disconnect (an electrical device)" , "Disconnect from power" , "Remove power from" , "Remove from a socket" , "Remove a blockage from" .)