Lowest point of wire exposed below new plug (5)
I believe the answer is:
nadir
'lowest point' is the definition.
(I've seen this before)
'wire exposed below new plug' is the wordplay.
'exposed' indicates the central letters (the inside of the word is exposed).
'below' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'plug' becomes 'ad' (as in plugging a product).
The centre of 'wire' is 'ir'.
'n'+'ad'='nad'
'ir' after 'nad' is 'NADIR'.
'of' is the link.
(Other definitions for nadir that I've seen before include "Drain (anag)" , "deep despair" , "Low point" , "Floor of drain in need of repair" , "lowest of the low" .)