A wiring structure improvement of an insulation piercing connector for electrical connection after plural signal lines (40) being inserted includes a connector body (1), plural terminals (2) disposed in the connector body (1), and a rotary cable coupler (3). The connector body (1) has a wiring end (11). Each of the terminals (2) has a terminal body (20) and a piercing member (21) formed at one end of the terminal body (20) and disposed at the wiring end (11). The rotary cable coupler (3) is sleeved around the wiring end (11) and has plural plug holes (30) corresponding to the piercing members (21). Thus, when the rotary cable coupler (3) is rotated, the signal lines (40) are pushed by the plug holes (30) towards the piercing members (21) correspondingly such that the piercing members (21) pierce the signal lines (40) for the electrical connection.