If both sides score the same number of wounds roll a dice each to see who gains the upper hand, the highest score wins. If both scores are the same neither side wins and the combat really is drawn as detailed later.
Tiebreaker (Moral High Ground)
Source: Core Rulebook 3E, p. 67
If both sides inflict equal wounds, each rolls a dice to see who gains the upper hand; equal rolls mean the combat is drawn.