FYI FORD - MustangSteve's Ford Mustang Forum
The Internet's Most Knowledgeable Classic Mustang Information
IF YOU HAVE A QUESTION ABOUT CLASSIC FORD MUSTANGS, YOU HAVE COME TO THE RIGHT PLACE!
MustangSteve has over 30 years of Mustang experience, having owned 30 of them and restored several others. With the help of other Mustangers, this site is dedicated to helping anyone wanting to restore or modify their Mustang.... THERE ARE NO DUMB QUESTIONS!!!!!
Visit MustangSteve's web site to view some of my work and find details for:
FYIFORD Contributors' PICTURES - Power Brake Retrofit Kits for 65-66 Stangs - Classic Mustang FAQ's by MustangSteve - How to wire in a Duraspark Ignition - Mustang Ride Height Pictures and Descriptions - Steel Bushings to fit Granada Spindles to Mustang Tie Rods - Visit my EBAY store MustangSteve Performance - How to Install Granada Disc Brakes MustangSteve's Disc Brake Swap Page - FYIFORD Acronyms for guide to all the acronyms used on this page - FYIFORD Important information and upcoming events

You are not logged in. Would you like to login or register?

  • Index
  •  » FYI Ford, Classic Mustang Tech Discussion
  •  » Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    • 1 of 1

       

    6/24/2026 3:25 PM  #1

    gkm24
    FYI Addict

    Offline

    From: Winchester, Hampshire, England
    Registered: 6/08/2013
    Posts: 116

    Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    Just fitted an Auto Meter speedo in my 66 with the EFI and AOD mod but not sure about wiring it up. Auto Meter state that the "Ford E9TZ-9E731-A" speedo sensor needs the low wire  grounded and the Hi side signal wire connected to the Speedometer. Thats easy enough,
    I am happy to do that but if the ECU needs a VSS (Vehicle Speed sensor) signal, does it need a pos and neg and if so, can I just wire it the same way as the speedometer?
    Thanks for any help.

     

    6/24/2026 5:19 PM  #2

    50vert
    Senior 24-7 FYI Addict

    Offline

    From: QLD Australia
    Registered: 4/01/2013
    Posts: 1,503

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    What ECU setup are you using? I guess a ford OBD1 ECU. Even my computer controlled AOD-E doesn't have a VSS input to the ECU.
    If you have something exotic, I think the autometer speedo has a VSS pass through.

    "Those telephone poles were like a picket fence"
     

    Yesterday 2:05 AM  #3

    gkm24
    FYI Addict

    Offline

    From: Winchester, Hampshire, England
    Registered: 6/08/2013
    Posts: 116

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    Thanks for your reply. You are correct in the ECU model. I just assumed  from the wiring diagram that as the ECU was shown with pin 6 -ve and 3 +ve for VSS that it needed the signal. Happy days if thats not needed then and I will just wire the speedo.

       •Thread Starter
     

    Yesterday 3:50 AM  #4

    50vert
    Senior 24-7 FYI Addict

    Offline

    From: QLD Australia
    Registered: 4/01/2013
    Posts: 1,503

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    Just to double check, (I didn't make my harness) I'd wait for second opinion from someone running a Fox ECU.
    I know that Dan (Nos681), uses a VSS with a cable on his Fox swapped car, he'll be along shortly.
    Was it a running car before the speedo swap?

    "Those telephone poles were like a picket fence"
     

    Yesterday 5:58 AM  #5

    gkm24
    FYI Addict

    Offline

    From: Winchester, Hampshire, England
    Registered: 6/08/2013
    Posts: 116

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    The whole thing is a refit of engine box speedo etc... Everything works fine but no signal to the speedo as I have the sensor connected to the ecu.
     

       •Thread Starter
     

    Yesterday 11:31 AM  #6

    Nos681
    Senior 24-7 FYI Addict

    Offline

    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,575

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    https://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif


    The Ford VSS connects to ECM pins 3(+) and 6 (-).
    Cruise control or a speedometer that requires the use of the VSS just taps into the same ECM pins.

    Assuming you are still using the A9P ECM.

    My ‘92 had the ECM and factory cruise control module share the single VSS signal.

    Last edited by Nos681 (Yesterday 11:42 AM)

     

    Yesterday 11:38 AM  #7

    Nos681
    Senior 24-7 FYI Addict

    Offline

    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,575

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    In simple terms, the VSS generates a signal the ECM uses for making adjustments.
    Having the correct speedometer gear could make a difference too.


    Last edited by Nos681 (Yesterday 2:42 PM)

     

    Yesterday 11:39 AM  #8

    Nos681
    Senior 24-7 FYI Addict

    Offline

    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,575

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

     

    Yesterday 2:37 PM  #9

    Nos681
    Senior 24-7 FYI Addict

    Offline

    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,575

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    I looked up Auto Meter instructions and bottom of page 3 appears to be your application.
    Read the note about connecting to the High signal wire.
    I would not ground the Low signal wire.
    I believe the ECM does it internally.

    I used Summit Racing listed instructions:

    https://static.summitracing.com/global/images/instructions/atm-3989_instructions.pdf



    Last edited by Nos681 (Yesterday 2:38 PM)

     

    Yesterday 3:28 PM  #10

    gkm24
    FYI Addict

    Offline

    From: Winchester, Hampshire, England
    Registered: 6/08/2013
    Posts: 116

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    Thank you for that. I do have it wired as in the diagram for 2 wire no computer involved. I will recheck the calibration as I know that I have not run the car for the recommended 2 mile distance yet. I guess if the ECM earths the signal, its all covered correctly but Auto Meter say that the HI side signal wire goes to the speedo. Is that the +ve wire or -ve wire or does it not matter. If it doesn't work I can swap it round I suppose

       •Thread Starter
     

    Yesterday 7:10 PM  #11

    Nos681
    Senior 24-7 FYI Addict

    Offline

    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,575

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    Look at page 19, it shows the pin polarity for VSS.

    Also notice that pin 3 and 6 for VSS is not listed in connector pinout on page 18.

    Veryuseful.com had the pinout connection in the drawings…colors may vary due to year and may not match…Ford engineering wisdom.

    Colors for foxbody changed a few times.

    https://www.jegs.com/InstallationInstructions/300/397/397-M-12071-A50.pdf?utm_campaign=10078&utm_source=impactradius&utm_medium=affiliate&clickid=xyGWyC0khxyPTkLQHL06m3z6UkF0mtUorxoFwc0&irgwc=1&utm_content=Skimbit%20Ltd._xyGWyC0khxyPTkLQHL06m3z6UkF0mtUorxoFwc0_487382_ONLINE_TRACKING_LINK_



    Hope this helps.

    Last edited by Nos681 (Yesterday 7:10 PM)

     

    Yesterday 7:15 PM  #12

    Nos681
    Senior 24-7 FYI Addict

    Offline

    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,575

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    50vert wrote:

    Just to double check, (I didn't make my harness) I'd wait for second opinion from someone running a Fox ECU.
    I know that Dan (Nos681), uses a VSS with a cable on his Fox swapped car, he'll be along shortly.
    Was it a running car before the speedo swap?

     
    Thanks Barry, had to clear cobwebs from my head to find this.
    I moved and good luck finding my notes.😁

     

    Today 4:14 AM  #13

    gkm24
    FYI Addict

    Offline

    From: Winchester, Hampshire, England
    Registered: 6/08/2013
    Posts: 116

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    Thank you both for the trouble you have taken to help me out. I really apreicate it.
    Regards,
    Graham.

       •Thread Starter
     

    Today 4:33 AM  #14

    Nos681
    Senior 24-7 FYI Addict

    Offline

    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,575

    Re: Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    Glad to assist.

    Please let us know the results.

     

     

    1 of 1

  • Index
  •  » FYI Ford, Classic Mustang Tech Discussion
  •  »  Does ECU need a pos and Neg supply for the speed sensor pins 3 and 6?

    • Board footera


    REMEMBER!!! When posting a question about your Mustang or other Ford on this forum, BE SURE to tell us what it is, what year, engine, etc so we have enough information to go on.