Speedometer signal info from Holley:

To enable a speed signal output:

Upload the Transmission ICF and check mark "Speedometer Output Enable".
Enter the correct Speed Calculation parameters (Tire Diameter & Rear Gear Ratio).
You'll also need to select the "Speedo" Output Type PWM+/− in the Inputs/Outputs screen.
This creates a +12V square wave Output that can be used to trigger an electronic speedometer.
The "Speedo" Output must be Pin Mapped to an available "P+" or "P−" pin on Connector J1(B), J2(B) or J3.
I realize the Transmission ICF Speedometer Output is displayed as PWM+/− (depending on the Output Type
selected in the Inputs/Outputs screen), but the ECU outputs this as a +12V square wave "Speedo" signal.
This is a Pulses Per Mile output signal, not PWM+/−. Pin Map the Output & connect it to your speedometer.