Why wont the psi and volts gauge work on the instrument panel in my 97 catera

NO , there is not a fuse just for those two thing's ! There are two power supply's for the whole insturment cluster . You could need a new cluster or the ECM isn't sending this info. to the cluster . Could have DTC'S - diagnostic trouble codes stored in the PCM or the insturment cluster . Without knowing how this works (insturment cluster gets it's info.) Your best bet , take it to a qualified repair shop that has the knowledge and test equipment to diagnose this problem.
Engine Oil Pressure Gage
The instrument panel cluster (IPC) displays the engine oil pressure as determined by the engine control module (ECM). The IPC receives a serial data message from the ECM indicating the engine oil pressure. The engine oil pressure gage defaults to 0 psi (0 kPa) or below if:
• The ECM detects a malfunction in the engine oil pressure sensor circuit.
• The IPC detects a loss of serial data communications with the ECM.
For the 4.2L LL8, the ECM uses an engine oil switch that is open when the oil pressure is normal and closed when the oil pressure is low. At normal pressure, the engine oil pressure gage will display 275 kPa (40 psi). At low pressure, the gage will go to 0 kPa and the low pressure warning will be displayed in the driver information center (DIC). At high pressure, the gage will display 551 kPa (80 psi). Any values between these three values are calculated values determined by the ECM.

Voltmeter
The instrument panel cluster (IPC) displays the vehicle voltage based on the information from the body control module (BCM). The IPC uses the serial data information from the BCM to provide a voltage level indication on the voltmeter.

DTC P0521: Engine Oil Pressure (EOP) Sensor Performance

DTC P0522 Engine Oil Pressure (EOP) Sensor Circuit Low Voltage
DTC P0523 Engine Oil Pressure (EOP) Sensor Circuit High Voltage

Volt Gage Inaccurate or Inoperative
2
Install a scan tool.
Turn the ignition ON, with the engine OFF.
With the scan tool, perform the instrument panel cluster (IPC) gauges output control.
Does the volt gauge move up and down when commanded?

Instrument gauges need to be supplied by a stable voltage in order to be reasonably accurate and because the vehicle battery voltage fluctuates quite a lot it would be useless to operate gauges.
It is for that reason a voltage stabiliser is used and generally mounted on the printed circuit board of the instrument panel. Assuming the supply to the panel is good and there are no other wiring or connection faults the instrument voltage regulator has probably failed.

In the early days the regulator was an electro-mechanical unit but for many years a semiconductor regulator has been used to stabilise the output voltage. Any voltage lower than the lowest battery voltage will theoretically serve but I find most are either 5 volt or 10 volt.

Certainly it seems you must remove the instruments and apply your trusty voltmeter...

There where many problems with the gauges in this year, pull the cluster out and send it in to be rebuilt.

with the ignition key off, press the "trip" button on the instrument panel, and while holding the button, turn on the ignition. the panel will do a self test of all lights and indicators. if the ones in question don't work, then it is a problem with the instrument panel itself. if they work, then you can look for shorted wires. I have technical info for most chrysler products so if it turns out that you need wiring diagrams or pinouts etc, I'm your man. good luck

check fuses

The oil sending unit is located on the engine block behind the drivers cylinder head area.You have to climb up on the motor to see it cause it is hard to see behind the wiring harness.You may also want to purchase a new sending unit because it is very long and you might need to buy the sending unit socket to replace it.Hope this helps.Good luck.

It could be a bad Starter Solenoid or Starter, or even a weak Alternator that is not fully charging the Battery when the engine is running. Make sure all connections to the Battery and Starter are tight and there is no corrosion present. Make sure the battery is fully charged and if your car is running your Alternator is at least showing 13 to 14 volts on a Volt Meter, or your Instrument Panel Gauge. Check that your Alternator Belt is tight too.

generally when half the cluster fails it points a a failed instrument cluster, Not the ECU. Either way I would have it diagnosed properly before you replace anything.

while installing the pannel you must have jarred or unplugged a connector . look around the top and side of the steering colume .

check your instrument panel fuse in the fuse box, the instrument cluster is operated by the same circuit