Like motorist’s hi-fi: not right for an ancient person (4)
I believe the answer is:
inca
'person' is the definition.
Both the definition and answer are singular nouns.
Maybe there's a link between them I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for inca that I've seen before include "Pre-conquest South American people" , "Old South American native" , "Ancient Andean Indian" , "Ancient civilisation of Peru" , "Pyramid builders" .)