Shift indicator lights up but does not display which gear I am in.

Check The fuses

The standard instrument cluster contains a microprocessor. The instrument panel cluster (IPC) microprocessor communicates with other controllers in the vehicle over the Class 2 serial data bus. The information passed over the Class 2 bus, along with direct external connections to other controllers and devices provides the inputs that are used to operate all of the gauges and the illuminated displays in the cluster. Some displays and gauges are operated directly by external sources (devices or controllers) and others are under software control of the IPC. As the IPC microprocessor runs the operating software, the microprocessor continuously processes Class 2 data in order to determine the correct values and states to display.


PRNDL Indicator (Park Reverse Neutral Drive Low)
The PRNDL display is a variable function electronic display located in the IPC. The PRNDL display is capable of displaying PRND321. The display electronically illuminates, or lights the back of the desired character in order to indicate the gear selection in the transmission. The IPC controls the PRNDL by use of the Class 2 messages that are received from the PCM/VCM. The vehicles with automatic transmissions have an electronic park reverse neutral drive low (PRNDL) range indicator. The system uses the signals from the neutral safety back up (NSBU) switch on the side of the transmission. Signals from this switch determine which LED is in the electronic PRNDL will light. The system is electronic. No internal adjustment is needed. Refer to Transmission/Transaxle for diagnostic information.

PRNDL Display
The IPC - instrument panel cluster displays the selected gear position as determined by the PCM.- engine computer . The IPC receives a class 2 message from the PCM indicating the gear position. The PRNDL display blanks if:
• The PCM detects a malfunction in the transmission range switch circuit.
• The IPC receives a class 2 message indicating the park position and the column park switch indicates a position other than park (open input).
• The IPC detects a loss of class 2 communications with the PCM. - class 2 communication is a network for the control modules to share information on .

Turn ON the ignition, with the engine OFF.
Place the shift lever in the PARK position.
Does the PRNDL display identify the PARK position?
YES - NO ?

Install a scan tool.
With the scan tool, observe the Park Switch Parameter in the IPC Inputs data list.
Does the scan tool display Closed?

Your best bet , take it to a qualified repair shop.

transmission mode selection switch failing.

there is a light bulb under the top cover

The light comes on automatically with the headlioghts, so you may have a burnt out bulb or a wiring problem.

The gear shift lever indicators tell you what gear you have an automatic transmission in on your vehicle. The shift solenoid tells the transmission when to shift gears and what gear to shift into. Newer model automatic transmissions have electronic shift solenoids that are activated and change gears based on the speed the vehicle is traveling. Troubleshooting either one of these transmission components is relatively easy if you know a little about automobile mechanics. With the right tools, you can determine whether the transmission shift solenoid is having a problem. Gear shift indicator problems can be determined simply by moving the gears into their designated position.
Transmission Shift Solenoid

• 1 Raise each corner of the vehicle up with the car jack and place jack stands under the frame. Make sure the car is raised high enough so you can work under the car freely.
  
• 2 Slide the drain pan under the transmission fluid drain plug. Remove the drain plug with a ratchet and socket, and let all the fluid drain out of the transmission. Remove the transmission pan bolts with a ratchet and socket. Pull the pan away from the bottom of the transmission, revealing the transmission shift solenoid.
  
• 3 Wipe off the shift solenoid with a shop towel. Disconnect one of the two plugs that attaches to the shift solenoid. Turn the knob on the volt meter to the ohms setting, so resistance can be measured. Set the volt meter on 200.
  
• 4 Take the black lead of the volt meter and touch the negative battery terminal wire. Take the red lead of volt meter and slide the tip into the terminal plug you just disconnected from the shift solenoid. Look at the reading you get on the digital display of your volt meter. Determine if the reading is between 12 and 25. Readings below 12 or above 25 tell you that the shift solenoid is not working. Reattach the plug to the shift solenoid and pull the second plug attached to the solenoid. Perform the same procedures on this plug wire. Replace the transmission shift solenoid after determining it is bad.
  

Gear Shift Indicator

• 1 Move the gear shift into the desired gear. Look at the gear labels and the arrow, or other indicator, to see if the gear shift indicator lines up with the selected gear.
  
• 2 Move the gear lever to another gear and look to see if the indicator lines up with the selected gear. Misalignment of the arrow will tell you if there is a problem. Moving the gear shift to "neutral" but having the indicator show the transmission is in "drive" tells you the gear shift indicator is not working properly.
  
• 3 Try each gear position to determine how much misalignment is in the indicator. Slide under the car and check for a loose gear shift cable. Check all the gear shift cable connections to ensure they are all tight and are not missing. Tighten any loose gear shift cable clamps or bolts. Replace the gear shift cable if you find that this is causing the misalignment with the gear shift indicator.
  

There should be some screws to remove the outside cover of the gear shift. Then the shift indicator P,R, N, D, etc should snap off. Then there is the light bulb housing underneath that indicator.

I had the same problem. They need to change the whole shift indicator assembly. Had mine fixed inn 30 minutes

If you are mechanically inclined, recommend that you remove the shift handle and check the internal components first. Might want to also begin checking the transmission fluid level.
https://www.youtube.com/watch?v=zuCNZhwIne0
Hope this helps