1999 Jeep Grand Cherokee; has demons!

The symptoms you are describing point to a communication problem. Your model of vehicle is equipede with a Chrysler Collission Detection Bus which has two lines one is (+) and the other one is (-). The plus one is violet with a brown tracer, the other one is white with a black tracer. Each of the wires should have about 2.5 volts when the ignition key is on. Check voltage, if voltage in any of these two wires is 0, check continuity to ground. If you find continuity to ground you have got a short to groung and you must trace it and repair it. Both lines are twisted and connect The Body Control Module BCM, Driver Door Module, Radio, Overhead Console, Powertrain Control Module PCM, Instrument Cluster, Vehicle Information Center,... Radio Controls on the steering wheel send signal to the BCM Through the CCD Bus and the BCM sends it to the Radio. If the CCD bus is not operational the radio will not respond to the steering wheel radio control switches. On the other hand, The PCM comunicates with the Instrument Cluster via the CCD Bus and if again this bus is not operational, then none of the gauges will work. To locate the wires of the CCD Bus, just unplug one of the mentioned modules and look for the wires with the colors I have described and perform the tests: Shorts to ground, shorts to Battery voltage, shorts between both wires. By the way if you find 123 ohms continuity between both wires it is ok. If you find a short to ground in the wire and not in a module, try to locate if the short is in a particular part of the bus, in that way, if that was the case you can always run a new pair of wires should you not want to remove the old ones, just cut the faulty ones.