One group in difficulty that's always ready to ignite (5,5)
I believe the answer is:
pilot light
'always ready to ignite' is the definition.
I can't judge whether this defines the answer.
'one group in difficulty' is the wordplay.
'one' becomes 'i' (Roman numeral).
'group' becomes 'lot'.
'in' indicates putting letters inside.
'difficulty' becomes 'plight' (plight is a kind of difficulty).
'i'+'lot'='ilot'
'ilot' placed into 'plight' is 'PILOT LIGHT'.
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for pilot light that I've seen before include "Burning 27 [GAS]" , "ignition system" , "It burns all the time" , "gas burner" , "Indicator" .)