This information applies to installing & programming a stand-alone VSS sensor with the Holley Avenger, HP & Dominator EFI.
To connect up to 4 Inputs & Outputs to the EFI main harness, use the Holley 558-400 I/O Auxiliary Harness.
If you're controlling an electronic transmission with a Dominator EFI, you must use that transmission's OEM VSS sensor.

If you have a cable driven speedometer, I highly suggest using an Auto Meter 5291/5292 Hall-Effect VSS sensor with your new Holley EFI.
The Auto Meter 5292 VSS requires a modification for use with a Fox Mustang speedometer cable end. Do not modify the speedometer cable.
The brass tube inside diameter must be drilled out to 17/32" or 35/64" (measure the retaining rib on the speedometer cable's metal end cap).
Only drill down into the brass tube far enough to insert the retaining clip! I drilled a little further so I could add an o-ring for leak prevention.

The 16 pulses per revolution has excellent resolution for good signal at very slow speeds.
Also, it's a durable aluminum construction, as opposed to the plastic VSS sensor I previously used.
(I'm not using shielded wiring.) It works great on the Data Monitor, Datalogging and for Math Channels.
I find it very useful to know the vehicle speed (MPH), when reviewing a datalog for tuning purposes.
VDO also sells 5-28V Hall-Effect VSS sensors: LINK (#340013 FORD 90°), LINK (#340011E GM 90°), LINK (#340011 GM straight).

When you setup the VSS parameters (I/O Digital Speed Input), there are a couple of caveats:
1) Start with the same number of "Pulses to Average" as "Pulses" (PPROT - pulses per rotation).
2) "Gear Ratio" - You must divide the rear axle gear ratio by the speedometer gear ratio (if you have a speedometer drive gear and a speedometer driven gear).
First divide the speedometer driven gear tooth count, by the speedometer drive gear tooth count, then divide the rear axle gear ratio by that number.
Unfortunately, this isn't in the Holley EFI instruction manual, so I'm informing you here.

Example VSS #1: A speedometer drive gear has 13 teeth, and the driven gear has 33 teeth (33 ÷ 13 = 2.54 speedometer gear ratio).
The rear axle gear
ratio is 4.10, which becomes a final EFI "Gear Ratio" of 1.61 (4.10 ÷ 2.54 = 1.61 "Gear Ratio" in EFI software).
Example VSS #2: A speedometer drive gear has 8 teeth, and the driven gear has 21 teeth (21 ÷ 8 = 2.63 speedometer gear ratio).
The rear axle gear
ratio is 3.31, which becomes a final EFI "Gear Ratio" of 1.26 (3.31 ÷ 2.63 = 1.26 "Gear Ratio" in EFI software).

Driveshaft Speed - This VSS sensor can also provide a Driveshaft Speed input by splitting the signal wire to a 2nd Digital Speed Input (RPM).
Example #1: Divide 16 sensor pulses per revolution, by 2.54 speedometer gear ratio, and enter 6.30 PPROT (16 ÷ 2.54 = 6.30 PPROT).

Example #2: Divide 16 sensor pulses per revolution, by 2.63 speedometer gear ratio, and enter 6.08 PPROT (16 ÷ 2.63 = 6.08 PPROT).
Currently, the PPROT parameter doesn't accept decimal values, however, it will in a future update.

Math Equation: Driveshaft RPM = MPH x 1056 x Rear Gear Ratio ÷ Tire Diameter x 3.1415 (Pi)
Holley EFI Math Channel, Driveshaft RPM: (1056/(25.6*3.14))*[VSS Sensor]*3.31 (Driveshaft RPM to Miles Per Hour) (Wheel RPM & Driveshaft RPM Calculator) (RPM/Driveshaft Calculator) (Holley EFI Datalogger Math Channels)

Some of the VSS parameters are "math operations" that occur on hardware vs the base firmware in the ECU.
They are performed when you key-on only. Meaning when you change it (click "Save"), it won’t recognize the change until you do a key-on event.
When you change some values with the key on, the math is incorrect because certain parts don’t get re-initialized, until the next key-on event.

If the I/O menu icon (ICF) isn't already uploaded (added) to the top Toolbar, follow these instructions:
(This same procedure applies to all the various Individual Configuration menu icons/items.)
The "I/O" function is an "Individual Configuration" of the Holley EFI software.
At top of screen, Click "Toolbox" and "Add Individual Config".
At top of new window, select "Individual Configuration Library".
At bottom of new window, select "Holley EFI Inputs/Outputs Config".
Select "I/O" and open "Base Config -".
The "I/O" icon will then be present at top of screen.
After creating the new Input, "Pin Map" it to an available ECU connector input pin. (How To Create A Custom Input/Output)

To connect up to 4 Inputs & Outputs to the EFI Main Harness, use I/O Auxiliary Harness 558-400.
Eight Wire I/O Auxiliary Harness Connector Pin-Out (also in the Holley EFI Wiring Manual - LINK):
Pin A...A12...White/Blue (Input #1) F,5,2,T,H,G
Pin B...A3....White/Red (Input #2) F,5,2,T,H,G
Pin C...A13...White/Black (Input #3) F,5,G
Pin D...A4....White/Green (Input #4) F,5,G
Pin E...B12...Gray/Yellow (Output #1) H,P+
Pin F...B11...Gray/Red (Output #2) H,P+
Pin G...B10...Gray/Black (Output #3) G,P−
Pin H...B3....Gray/Green (Output #4) G,P− (Holley 558-400 I/O Auxiliary Harness Instructions)
The 558-400 I/O Auxiliary Harness is 20 feet long, and it's "plug & play" into the EFI main harness.