In France source of happiness is right to vote (9)
I believe the answer is:
franchise
'right to vote' is the definition.
('franchise' can be a synonym of 'right to vote')
'in france source of happiness is' is the wordplay.
'in' indicates putting letters inside.
'source of' says to take the initial letters.
The initial letter of 'happiness' is 'h'.
'h'+'is'='his'
'france' enclosing 'his' is 'FRANCHISE'.
(Other definitions for franchise that I've seen before include "Authorisation to engage in specific commercial activity" , "Rights assigned by authorisation" , "Authorisation to sell a company's goods or services in a specified area" , "The right to vote in elections" , "Dealership" .)