Nobleman seen in right tail lamp (4,5)
I believe the answer is:
rear light
'tail lamp' is the definition.
(synonyms)
'nobleman seen in right' is the wordplay.
'nobleman' becomes 'earl' (member of the nobility).
'seen in' indicates putting letters inside.
'earl' put into 'right' is 'REAR-LIGHT'.
(Other definitions for rear light that I've seen before include "retrospectively this is illuminating" , "Whereby vehicle may be seen" , "late display of driving" , "Stern glower" , "estate needs one" .)