Crazy main switch for the current (6)
I believe the answer is:
maniac
'crazy' is the definition.
(I've seen this before)
'main switch for the current' is the wordplay.
'switch' indicates an anagram.
'for' says to put letters next to each other.
'the current' becomes 'ac' (alternating current).
'main' with letters rearranged gives 'mani'.
'mani'+'ac'='MANIAC'
(Other definitions for maniac that I've seen before include "Mad (keen) type" , "Deranged person" , "Psycho" , "Lunatic, madman" , "fruitcake?" .)