Re: 99 Jeep Grand Cherokee
Welcome to the garage.
That you loose all indicators looks that you have a PCI data bus problem. The PCM sends data via this bus to the instrument panel. A problem in the PCM or any of the connected components can bring the bus down and the engine will stop. Sometimes water ingress in a large connector on the passenger side can bring the bus down as well. Not so easy to solve this one. To be sure that the bus has a problem, you could measure the voltage on pin 2 of the data connector under the steering wheel. Normal voltage is around 2.5 V. If its 0V, then or the bus wire is shorted to ground, or the PCM is not supplying the bus voltage. If its around 7.5V, then one of the connected components has a problem and causes the bus voltage to go too high.
There is a shorting plug under the steering wheel area where all the bus wires are connected. Removing the shorting plug will disconnect most of the components from the PCM, except the SKIM, which is necessary to be able to start the engine.
For the power steering to work, you need a running engine.
Also check for fault codes set using the key dance: ignition switch off/run three times and leave in run at the third time. Odometer will show Done when no faults stored, or a fault code(s). Let us know what it gives.