At first I was using the standard 3 wire speed sensor that was used in the 46RH in 1994. On the 46RH it goes into the speedo cable drive. On the Rams and Dakotas the PCM uses that signal for the cruise control, so it knows when to shift into OD and lockup the torque converter, and to run the speedometer.
But that speed sensor doesn't have a mechanical output for a speedometer, since the gauges in 1994 were all electronic. I didn't really feel like gutting my speedo and putting electronics in behind it, so I changed to an earlier 2 wire speed sensor like what would have been used in the late 80s. Check Standard Motor Products part # SC108. This meant I had to change my speedo cable to one with the smaller connector (I think from an 89 Dakota), but that wasn't a huge problem.
The later 3 wire speed sensors have one power wire from the PCM, the signal back to the PCM, and a ground. The 2 wire I'm using now just has a signal to the PCM and a ground. I was surprised it would work, but it does. I have heard the 2 wire sensors are less reliable than the newer 3 wire sensors, but I'm not too worried. The worst that would happen is I would lose OD and lockup, so I could still get the car home.
