A friend of mine had a similar problem on a 1994 and it turned out to be the
speedometer head (the part in the dash).

I believe by 1997 the speedo is electronic (like a tachometer), i.e. it
uses the VSS (vehicle speed sensor) signal to calculate the speed. This
is a pulse generator driven by the transmission. It puts out pulses,
and the vehicle speed can be calculated by the time between pulses- the
faster you go, the shorter the time between pulses. The cruise control
also uses this signal, in fact my '94 explorer has a mechanical speedo
but also has a VSS for the cruise control.

So- since your cruise control works fine (very smart of you to include
that bit of info) your VSS is obviously working. I'd can think of three
possible causes:

1. You have a bad connection in the VSS signal somewhere between your
speedo and the the point where the VSS signal to the speedo branches
off from the cruise control. This would be an intermittant open, not a
short, because a short would also kill the cruise control at the same
time.

2. Your speedo is not getting power, or has a bad ground. It's
electronic, so it needs power to amplify and process the VSS signal to
drive the speedo and odo.

3. A bad connection in the speedo assy- corrosion, a bad solder joint,
something like that.

Just because there are more things to go wrong, I'd guess the speedo
itself to be the most likely culprit. When you're driving down the road
and it stops working, try smacking the dash near the speedo with your
hand to see if jarring it makes it start working again.

Tracing out the wiring is a tough job, even getting access to them is
tough. In general, I'd expect the VSS wires to go from the transmission
to the cruise control, and then to the speedo. So you could inspect and
wiggle the connectors going to the cruise control under the hood, the
ones behind the dash are going to be very hard to access. As I said,
since the cruise control works, focus on the speedo and the wiring
between the cruise control and the speedo, the VSS and wiring from
there to the cruise control must be good.

Good luck,
-Paul

This happened to my '91 in, oh, about '96. The speedometer needle would
oscillate wildly back and forth, and after about a month of this just fell
to the peg and didn't move again. The cruise control and odometer still
worked fine, though. About two years later I hit a sharp bump and the
speedometer started working again - it has been fine ever since.