Sun in seventh house is in the house of his enemy Venus. The bright, cheerful and confident Sun is quite dominant and not suitable to graciously deal with the delicate matters of relationship, business-partnership, legal cases and contracts signified by the seventh house. But the bright side is Sun from seventh house casts an aspect on his own house which is the first house in horoscope. So that gives the native health, confidence and ability to deal with any difficulties in life. Possibly beautiful eyes also and skin problems especially if there is an enemy sign in first house.

      According to B. V Raman, natives with Sun in seventhhouse could be fair and have thin hair. Marriage is often delayed and troubled. He/She could also receive troubles through the government and possible humiliation. Seventh house deals with marriage. Any sort of malefics in seventh house suggests a troubled married life. If Sun is co-tenant with malefics like Mars, Saturn, Rahu or Ketu then that should send alarm bells ringing in marriage. Such natives should do the utmost to keep a compromising attitude when dealing with marriage partner. In all likelihood the marriage partner whether a male or female is confident, rash, egoistic and a little short on empathy. But along with that the marriage partner is also likely to be successful, influential and able to deal with crisis quite brilliantly. Ofcourse co-tenants and aspects also play a major role in defining the character of spouse but generally spouse is the more confident and more popular partner in marriage. 

     Sun is confident bordering on arrogance. So many a times natives are seen to be prone to self-flattery, arrogance and failing to empathize with others around. These pompous attitude could lead to troubles especially legal cases or problems in marriage or business-partnership. It is advisable to keep these bad traits in check for natives with Sun in seventh house. Also prayers to Lord Ganesha are ideal as he is God of wisdom. His actions and behavior are what made him first among Gods to be prayed (Pratham Pujya). Following his modest behavior along with his keen intellact would provide the desired success to those with Sun in the seventh house. 

References:

Raman, Bangalore Venkata. How to Judge a Horoscope. Delhi: Motilal Banarsidass, 2014. Print.