Bulb in contact with electrical current working finally (5)
I believe the answer is:
onion
'bulb' is the definition.
(plant bulb)
'in contact with electrical current working finally' is the wordplay.
'in contact with' becomes 'on' (to be on something is to be touching it).
'electrical current' becomes 'I' (physics symbol).
'working' becomes 'on' (on can mean working or activated).
'finally' is a charade indicator (letters next to each other) (some letters go at the end of others).
'on'+'i'+'on'='ONION'
(Other definitions for onion that I've seen before include "Aromatic flavourful versatile vegetable" , "Cause of tears" , "Head (slang); vegetable" , "Tear-jerking bulb" , "Strong tasting vegetable" .)