Guide present source of power (6,7)
I believe the answer is:
direct current
'power' is the definition.
(direct current is a kind of power)
'guide present source' is the wordplay.
'guide' becomes 'direct' (synonyms).
'present source' becomes 'current' (I have seen 'Source of power' mean 'current' so perhaps 'source' could also mean 'current'. I am not sure about the 'present' bit.).
'direct'+'current'='DIRECT CURRENT'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for direct current that I've seen before include "Electrically, DC" , "Electrical flow in one direction only" , "potentially shocking!" , "Electricity flowing in one direction only" , "Electricity flow from, eg, battery" .)