Travelled in support of chosen conductor (9)
I believe the answer is:
electrode
'conductor' is the definition.
(electrode is a kind of conductor)
'travelled in support of chosen' is the wordplay.
'travelled' becomes 'rode' (I've seen this in other clues).
'in support of' means one lot of letters go next to another (I've seen this in other clues).
'chosen' becomes 'elect' ('elect' as an adjective can mean chosen).
'rode' after 'elect' is 'ELECTRODE'.
(Other definitions for electrode that I've seen before include "Conductor making contact in a circuit" , "Connecting conductor" , "Conductor by which current enters" , "Terminal of, eg, an acid battery" , "Conductor for electricity as it enters or leaves" .)