Cold lighting unpopular with motorists! (6)
I believe the answer is:
clamps
'motorists' is the definition.
Although both the answer and definition are plural nouns, I don't see how they can define each other.
'cold lighting unpopular' is the wordplay.
I cannot really understand how this works, but
'cold' could be 'c' (eg on taps) and 'c' is found within the answer.
The remaining letters 'lamps' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'with' acts as a link.
Can you help me to learn more?
(Other definitions for clamps that I've seen before include "Holds tightly with device - illegally parked cars? (6)" , "Grips" , "fasteners" , "Devices to hold things, car wheels say" , "Devices to hold things firmly, car-wheels say" .)