Conductor when chosen went up (9)
I believe the answer is:
electrode
'conductor' is the definition.
(electrode is a kind of conductor)
'chosen went up' is the wordplay.
'chosen' becomes 'elect' ('elect' as an adjective can mean chosen).
'went up' becomes 'rode' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'elect'+'rode'='ELECTRODE'
'when' is the link.
Can you help me to learn more?
(Other definitions for electrode that I've seen before include "Conducting point by which electric current enters or leaves" , "Conductor (eg, in battery)" , "Conductor for electricity as it enters or leaves" , "Conducting terminal" , "Conductor making contact in a circuit" .)