Conversation so far:
How did Ross Brawn's career get started?
Ross Brawn's career in motorsport began in 1976 when he joined March Engineering in the town of Bicester as a milling machine operator.
How did Ross Brawn do with March Engineering?
Soon afterwards Ross Brawn joined their Formula 3 racing team as a mechanic.
How long did Ross Brawn work as a mechanic?
Ross Brawn was a mechanic until 1978, when he joined the Williams Grand Prix Engineering team.

Question: What did he do there?
Self-contained rewrite: What did Ross Brawn do with the Williams Grand Prix Engineering team?