My speedommeter doesn't work but my cruise control does. Is it cable driven or electric?

It's probably a problem with cruise control module , located under the hood in engine compartment . Or a bad connection somewhere . Do you know how to do electrical testing ? Is the air bag light lit on the instrument cluster ?

Could have DTC'S - diagnostic trouble code's stored .
DTC P1554
The powertrain control module (PCM) inhibits cruise control operation when certain conditions are not appropriate for cruise control operation. The PCM removes the ground from the cruise control inhibit signal circuit in order to disengage cruise control operation.
DTC P1585
Output driver modules (ODMs) are used by the powertrain control module (PCM) in order to turn on many of the current driven devices that are needed to control various engine and transaxle functions. DTC P1558 set indicates that an improper voltage level has been detected on the signal circuit which controls the cruise control inhibit circuit.
Action Taken When the DTC Sets
• The PCM will not illuminate the malfunction indicator lamp (MIL).
• The PCM will store the conditions present when the DTC set as Failure Records data only.

Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions. However, steep grades may cause variations in the selected speeds. The electronic cruise control system has the capability to CRUISE, COAST, RESUME SPEED, ACCELERATE, and TAP-UP or TAP-DOWN.
The main parts of the cruise control system are:
• The cruise control module assembly
• The function control switches
• The cruise control release switch
• The clutch pedal position switch (CPP), if equipped
• The stop lamp switch assembly
• The vehicle speed sensor
The cruise control system uses the cruise control module assembly to maintain the desired vehicle cruise speed and operation. The cruise control module assembly has an electronic controller and an electric stepper motor to vary the throttle in each different cruise control mode. The electric controller monitors vehicle speed and operates the electric stepper motor. The stepper motor operates in response to the electronic controller, to maintain the desired cruise speed. The electric stepper motor moves a strap that is attached to the cruise control cable which moves the throttle linkage. The cruise control module assembly contains a low speed limit which will prevent system engagement below a minimum speed of 40 km/h (25 mph). The module assembly is not serviceable.

Check your cruise control fuse.

have a look at the cruise control cable that goes next to your throttle cable next to your throttle body for looseness

The adjustment of the brake light switch or it could be bad. the brake lights can work fine and the part of the switch that works the cruise doesn't The swiches that control it from the steering wheel can losse connection in a part called the clock spring. Vacume connections can effect the cruise but yours is likly cables less therefore doesn't work the cruize.

cruise control best let garage check out,here are few things to check,check fuse and check to see if brake lights dont work.check brake light fuse if fuse okay brake light switch could faulty or bad connection then brake light will reset cruise control you apply brakes.if all is good problem could be speed sensor or accelerator pedal to ecm.you need diagnostic euipment to troubleshoot.

The speedometer is electronic and controlled by a micro processor, the needle is operated by a special DC electric motor called a "stepper" motor, this little motor can cause this problem as well as the Vehicle speed sensor on the transmission (see photo below), either part can cause the problem, the cruise not working would lead me to believe the speed sensor is defective, but you should have a Check Engine light on and a fault code for the sensor, do you have either? Autozone and others do the fault code test for free, ask for an OBD2 fault test. Here is the picture of the sensor I mentioned.

The most common cause that I've seen on these vehicles is the cruise control switch. But before you replace this switch, I recommend disconnecting the battery for about 20 minutes. Note that I mean the battery in the trunk. All you need to do is take the negative (black) cable off and leave it off for about 20 minutes. If this doesn't help, the switch/stalk is the most common cause.

jnjkingbird, It sounds like this problem is the clock spring as I don't believe that the horn and the cruise control would share a fuse. However, they do share a circuit in the clock-spring. You can check for power at each unit (horn and the cruise control) which would confirm this. Check each fuse as well. Good luck with this.

Ok, the '03 Jeep Grand Cherokee uses a small vacuum line to control the servos. Since your light comes on, it's obviously getting power. 9 out of 10 times it's the vacuum hose.
Pop the hood and look on the passenger side towards the back for the engine coolant reservoir. It's most likely underneath it so you may have to remove the res. Check the vacuum hose and all vac. connections then check the electrical connections. If that's not the problem, check the cruise control connection to the throttle linkage.
If that still doesn't do it, you may need use scan tools and diagnostic procedures that are out of the scope of home mechanics.
Wish ya luck!