What’s the deal with Automotive Electronic/Programmable Speedometers?

One of the greatest features of the electric speedos is that they are fully programmable, which means you can recalibrate it rather easily if you happen to change your rear-end gear or tire sizes. If you have ever had to change the gear in the transmission to adapt for either of these changes, you will appreciate the ease of the calibration with this speedo. The overall calibration procedure is quite simple, with measuring the 2-mile distance for calibration being the critical point. To quickly reiterate what the instructions state in more detail, you need to make sure the tires are inflated to the manufacturer’s specs, and also try not to exceed 45 MPH, as tires will slightly increase in diameter with vehicle speed; this will aid in minimizing any error. Obviously, you do not want to break traction, either, as that will also adversely affect the calibration. And lastly, the load (weight) of the vehicle plays into the diameter of the tires, too, so be sure to have an average load in the vehicle during calibration.

Now, for the connections to various vehicles. We offer two styles of senders; one for most GM and most Chrysler (PN 5291), as they both share the 7/8″ – 18 THD, which will thread into the cable output on an earlier model transmission that may have used a cable previously. You would want to double check to make sure that this thread will match what you have on your transmission, to ensure compatibility. The other sender we offer is for most Ford transmissions (PN 5292) that have cable outputs, which utilize a retaining “clip” to mount the sender to the housing of the transmission. Both senders will replace the existing cable, or attach to the cable output of the transmission, to produce a signal to drive the speedometer. However, you guys with a later model transmission are saying, “Hey, I don’t have a cable”. Well, we’ve taken care of that, too. For most late model applications, our speedos can directly connect to the VSS (vehicle speed sensor) to derive the signal needed to operate, and show the vehicle speed. But, you will need to take this signal DIRECTLY from the VSS, and not from the computer, as the signal after the computer is buffered (conditioned) and our speedos will not recognize that type of signal, so the raw signal from the VSS is the wire to be connected to. Finding which wire is the signal is usually quite simple, as the signal wire will produce anywhere from 2v up to 120v DC peak to peak, so you can test for that signal with a standard multimeter (the voltage should increase with the vehicle speed). Otherwise, you can look in a service manual for the signal wire, or if you can’t find it anywhere, contact us and we’ll see if we have the information.

Onto the calibration procedure itself, the easy part. Current AutoMeter Speedometers use the Trip Reset Button as the calibration button, some earlier AutoMeter Speedometers use a separate calibration button. We include a pushbutton that is used for the calibration steps on models which require the separate button. Once you have everything installed and before you start the motor, follow these steps

  1. Press and hold the button while starting the vehicle. Once the motor is running, you can then release the button after the pointer goes to the highest MPH reading and stays.
  2. Drive to the beginning of your carefully measured 2-mile distance, and stop. Press the button again, and the pointer should then go to half of the maximum MPH reading, and the speedo is then ready to be calibrated.
  3. Drive the two miles, stop, and push the button, the pointer will drop to zero and the calibration is complete and the speedo should begin indicating the speed when you start driving.