Ford 2003 Mustang Workshop Manual page 531

Four Wheel Anti-Lock Brake System (4WABS) Hydraulic Control Unit (HCU)
NOTE: This procedure only needs to be performed if the 4-wheel anti-lock brake (4WABS) hydraulic
control unit (HCU) has been installed new or if the HCU lines have been opened.
1. Clean all dirt from and remove the brake master cylinder filler cap (2162), and fill the brake
master cylinder reservoir (2K478) with the specified brake fluid.
2. Connect a clear waste line to the RH rear bleeder screw (2208) and the other end in a container
partially filled with recommended brake fluid.
3. Loosen the RH rear bleeder screw until a stream of brake fluid comes out. While the assistant
maintains pressure on the brake pedal (2455), tighten the RH rear bleeder screw.
Repeat until clear, bubble-free fluid comes out.
Refill the brake master cylinder reservoir as necessary.
4. Tighten the RH rear bleeder screw, and disconnect the waste line.