This answer depends largely on what transmission and vehicle you have. For some the answer is easy, for others it is not impossible, but just not as easy. Please read on.
Most factory equipped speed sensors will operate our speedometer. If you are running a late model transmission in an early vehicle with no computer, then that is o.k. You will have two wires on most factory speed sensors. Ground the low-side signal wire and run the hi-side signal wire to the speedometer and calibrate. It’s just that easy.
Most GM transmissions such as TH350, TH400, 700R4, TH200, &TH250’s may use the AutoMeter # 5291 speed sensor. This will simply thread onto the transmission in place of where the cable used to go. Some Chrysler, AMC, & Jeep transmissions may use the same sender. To know for sure, look to see how the cable attaches to the transmission. If it uses a large 7/8” threaded nut, that threads onto the transmission, then you can use the #5291.
Most Ford transmissions use a cable the pushes into the transmission and use a small retaining clamp to hold it in. For these models use a model # 5292 AutoMeter speed sensor. You will transfer the O-ring, speedometer gear and the gear retaining clip from the speedometer cable to the speed sensor, then install the sensor into the transmission. Just like the GM style, some Chrysler, AMC, and Jeep products may use a Ford style cable. You will have to look at your cable at the trans to see how it installs to know which version you have.
Now, for those of you who have something different than what we have addressed and do not have any type of factory speed sensor, there is still a solution. You may use a universal type of Shaft Speed Sensor, which can be found at many different Speedometer specialty shops. This would be the same type of speed sensor that many after market cruise control systems have used over the years. If you can not locate a speed sensor, you may then contact us through the Ask A Question icon on our website and we can help you locate one.