Aid when driving in day time in Suffolk town (9)
I believe the answer is:
dipswitch
'aid when driving in' is the definition.
The definition suggests a singular noun which matches the answer.
'day time in suffolk town' is the wordplay.
'day' becomes 'd' (abbreviation for day).
'time' becomes 't' (abbreviation).
'in' means one lot of letters goes inside another.
'suffolk town' becomes 'ipswich' (I've seen this before).
't' put inside 'ipswich' is 'ipswitch'.
'd'+'ipswitch'='DIPSWITCH'
Can you help me to learn more?
(Another definition for dipswitch that I've seen is " dimmer".)