Mustang DIY

Mustang SpeedCal Info – FAQ Frequently Asked Questions



Mustang SpeedCal FAQ

All the information you need on installing and calibrating your new Dallas Mustang SpeedCal can be found here, if you need additional help please call us at 1-800-MUSTANG.

The Dallas Mustang SpeedCal is a highly flexible, easily adjustable electronic speedometer calibrator. With SpeedCal, you can maintain accurate speedometer readings with virtually any combination of rear tire size and gear ratio.

Time Required: Approximately 1 hour.
Tools Required: Basic hand tools, Multi-meter probe and the SpeedCal Ratio Multiplier Table.

Pre-installation Setup: Using the SpeedCal Ratio Multiplier Table, or the DMP SpeedCal worksheet, determine the correct ratio multiplier and enter the binary code into the SpeedCal. Then, attach the cover using the supplied screws. The picture below shows the dipswitch settings of 1001001000 for a 3.27 to 3.73 gear swap.

Mustang SpeedCal PreInstall

Mustang SpeedCal Installation Steps:

  1. Remove the vehicle negative battery cable.
  2. Inside the vehicle passenger compartment, remove the shifter knob, outer shift boot, and inner shift boot. It is generally easier to disconnect the cigarette and traction control (if applicable) switches from the plastic housing and set the housing aside to facilitate installation. The outer boot is merely snapped in place and can be easily removed by grasping firmly on each side of the shifter and pulling straight up and away from the console. The inner boot uses four 8mm bolts for attachment.
    Mustang SpeedCal Step 2
  3. Route the SpeedCal harness down the driver’s side of the transmission and re-install the inner boot. Route the SpeedCal harness to the back of the inner boot.Mustang SpeedCal Step 3
  4. Connect the Red wire of the SpeedCal to the cigarette lighter hot wire with the provided scotch lock. As an example, on a ’99 and up late model Mustang this should be a Blue/White wire.
    Mustang SpeedCal Step 4
  5. Center the SpeedCal ahead of the shifter and re-install the outer boot and shifter knob.
    Mustang SpeedCal Step 5
  6. Under the vehicle, locate and remove the YSS connector on the driver’s side of the transmission.
    Mustang SpeedCal Step 6
  7. Using a small flat bladed screwdriver or a thin punch, CAREFULLY remove the red contact lock inside the connector shell. CAREFULLY slide the screwdriver/punch down the side of each contact to disengage the contact retainer and remove both contacts from the connector shell.
    Mustang SpeedCal Step 7
  8. Place the VSS connector shell removed in the previous step onto the SpeedCal Blue and Green wires. Keying is not critical.
    Mustang SpeedCal Step 8
  9. Push the contacts into the connector shell until the contact retainers engage. Usually, a faint *click* will be heard for each contact retainer engagement. Reinsert the red contact lock.
    Mustang SpeedCal Step 9
  10. Reconnect the VSS connector that is now installed on the SpeedCal to the transmission.
    Mustang SpeedCal Step 10
  11. In the vehicle harness VSS wire pair, determine which of the two wires is the ground wire. On a late ’94-’98 model Mustang this should be a Pink/Orange wire, ’99 and up, this shuold be a gray/red wire.
    Mustang SpeedCal Step 11
  12. Find the supplied connector shell int he SpeedCal installation kit. Using the connector shell keys as a guide, align the ground wire so it will mate with the SpeedCal Gray wire when the two connectors are mated.
    Mustang SpeedCal Step 12
  13. Insert the remaining vehicle harness wire into the remaining connector location. Again, push the contacts into the connector shell until the contact retainers engage. A faint “click” should be heard upon engagement. Insert the supplied red key lock into the connector shell.
    Mustang SpeedCal Step 13
  14. Connect the vehicle harness to the SpeedCal connector. Insure the contacts align per Step 13. Tie the excess wiring and cable harness with the supplied E-Z Ties.
    Mustang SpeedCal Step 14
  15. Reconnect the battery terminal and drive the vehicle. Insure the vehicle speedometer is functional. If possible, pace the vehicle against a vehicle with a known reasonably accurate speedometer.


    • If the vehicle speedometer ever malfunctions, disconnect the vehicle negative battery terminal, wait approximately 30 seconds, and reconnect the battery. This is required to “cycle power” to the SpeedCal as the cigarette lighter is and unswitched accessory outlet.
    • When wired per these instructions, the SpeedCal is always powered. The SpeedCal power consumption is minimal, however, and will not introduce noticeable vehicle battery power drain. It should be noted that portions of the Vehicle EEC are also connected in this fashion so this is not an unusual installation procedure. If the installer desires to use a switched accessory outlet, consult the shop manuals particular to the target vehicle and choose a switched accessory signal to tie into. The SpeedCal will perform just the same from switched power as from unswitched power.
    • The DMP SpeedCal is capable of speedometer adjustments in increments of 0.2% and will provide accurate vehicle speed data above the displayed speedometer value (160 mph for a late model Mustang Cobra). In order to retain this accuracy care should be taken in determining the correct binary code as the SpeedCal cannot provide accurate speedometer readouts with an incorrect ratio multiplier selection.
    • The supplied ratio table will provide reasonably accurate ratio settings for a typical gear swap. For more information or help please call 1-800-MUSTANG.

Mustang SpeedCal Table
 (Link to PDF)

Mustang SpeedCalTable


About Tommie

It was 1997 when I got my first car, it was a 1989 Convertible Mustang that was handed down from my father. That is where my love of the Mustang began. We have had several Mustangs over the years, and I have come to appreciate all the generations, but that 5.0 still has a special place in my heart.

You must be logged in to post a comment Login