Current applied to RAM, causing malfunction (3,2)
I believe the answer is:
act up
'malfunction' is the definition.
(I've seen this before)
'current applied to ram' is the wordplay.
'current' becomes 'ac' (alternating current).
'applied to' is a charade indicator (letters next to each other).
'ram' becomes 'tup' (both can mean a male sheep).
'ac'+'tup'='ACT UP'
'causing' is the link.
(Other definitions for act up that I've seen before include "Behave badly (colloq.)" , "take part in heightened drama?" , "go wrong" , "Behave like a brat" , "Become unpleasant" .)