This article is from the Chrysler-Plymouth-Dodge FAQ, by Dr. David Zatz with numerous contributions by others.
There is a TSB out on this problem with the Shadow/Sundance. Take it to
your dealer, they should fix it for free. The TSB was issued in 1994. The
problem is the speed sensor connector; a new one must be spliced in.
Details from Neil Emiro on replacing the speed sensor yourself follow. They
probably apply to all K-based (and extended K-based) cars:
To get it out, you will need a 10mm wrench, a flat blade screwdriver, and
if your car has cruise, a 19mm wrench. Jack the car up. If you look
underneath at the oil pan plug, and look back on the car, to where the
axle goes into the tranny, you will see it. It's mounted in the top of
that extension housing. If your unit is round, just unplug it and remove
the cable if there is one, and pry it up, putting the screwdriver between
the black body of the sensor, and the natural color base. If your unit is
kind of short and diamond shaped, disconnect the wiring and cable, and
there's a 10mm bolt on the far side that you'll probably be able to feel
better than see.