The gas gauge, heat gauge, O.D., C/C, rear window defogger, heater, A/C, and seatbelts stopped working

System Description NEEL0216 MODELS WITHOUT POWER DOOR LOCKS NEEL0216S01 The rear window defogger system is controlled by the rear window defogger timer. The rear window defogger operates only for approximately 15 minutes. The rear window defogger switch is integral to the air control. Power is supplied at all times
to rear window defogger relay terminal 5
through 20A fuse [No. 25, located in the fuse block (J/B)]. With the ignition switch in the ON or START position, power is supplied
through 10A fuse [No. 5, located in the fuse block (J/B)]
to rear window defogger relay terminal 1, and
to rear window defogger timer terminal 1. Ground is supplied to air control (rear window defogger switch) terminal 8 and rear window defogger timer terminal 4 through body grounds M14 and M68. With the rear window defogger switch (located in air control) ON, ground is supplied
to rear window defogger timer terminal 3
through air control (rear window defogger switch) terminal 8. Rear window defogger timer terminal 2 then supplies ground to the rear window defogger relay terminal 2. With power and ground supplied, the rear window defogger relay is energized. Power is supplied
through terminal 3 of the rear window defogger relay
to rear window defogger terminal +. Rear window defogger terminal - is grounded through body ground R102. With power and ground supplied, the rear window defogger filaments heat and defog the rear window. When the system is activated, the rear window defogger indicator illuminates in the air control. Power is supplied
from rear window defogger relay terminal 3
to air control (rear window defogger switch) terminal 4. Air control terminal 8 is grounded through body grounds M14 and M68. MODELS WITH POWER DOOR LOCKS NEEL0216S02 The rear window defogger system is controlled by the smart entrance control unit. The rear window defogger operates only for approximately 15 minutes. The rear window defogger switch is integral to the air control. Power is supplied at all times
to rear window defogger relay terminal 5
through 20A fuse [No. 25, located in the fuse block (J/B)] and
to smart entrance control unit terminal 49
through 7.5A fuse [No. 28, located in the fuse block (J/B)]. With the ignition switch in the ON or START position, power is supplied
through 10A fuse [No. 5, located in the fuse block (J/B)]
to rear window defogger relay terminal 1 and
to smart entrance control unit terminal 27. Ground is supplied to air control (rear window defogger switch) terminal 8 and smart entrance control unit terminals 43 and 64 through body grounds M14 and M68. With the rear window defogger switch (located in air control) ON, ground is supplied
to smart entrance control unit terminal 14
through air control (rear window defogger switch) terminal 1. Smart entrance control unit terminal 37 then supplies ground to the rear window defogger relay terminal 2. With power and ground supplied, the rear window defogger relay is energized. Power is supplied
through terminal 3 of the rear window defogger relay
to rear window defogger terminal +.
Rear window defogger terminal - is grounded through body ground R102. With power and ground supplied, the rear window defogger filaments heat and defog the rear window. When the system is activated, the rear window defogger indicator illuminates in the air control. Power is supplied
from rear window defogger relay terminal 3
to air control (rear window defogger switch) terminal 4. Air control (rear window defogger switch) terminal 8 is grounded through body grounds M14 and M68

Doesn't use a relay , controlled by lift gate control module . Your best bet , take it to a qualified repair shop .
Rear Window Defogger System Components
The rear window defogger system consist of the following components:
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HVAC control module

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Liftgate module (LGM)/endgate module (EGM)

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Rear window defogger grid

Rear Window Defogger Operation (With LGM)
Battery positive voltage is supplied through the LGM 2 fuse to the LGM for the rear window defogger system. When the rear window defogger switch is depressed, the HVAC control module illuminates the rear window defogger indicator, and sends a class 2 message to the LGM to enable the rear window defogger. The LGM enables the rear window defogger by allowing battery positive voltage to the rear window defogger.
When the rear window defogger switch is pressed for the first time, the defogger cycle lasts 10 minutes. Further operation results in 10 minute defogger cycles.
DTC B0283 Electric Rear Defrost Circuit - do you know what DTC'S - diagnostic trouble code's are ?
Circuit Description
The liftgate module (LGM)/endgate module (EGM) monitors the voltage level on the supply voltage circuit of the rear window defogger. The LGM/EGM test the supply voltage circuit of the rear window defogger every 160 milliseconds. With the rear window defogger inactive, the supply voltage circuit of the rear window defogger will have no voltage present. With the rear window defogger active, the supply voltage circuit of the rear window defogger will be near system voltage.

As by heat only works some of the time , you mean it doesn't blow air out of the vent's . This means you probably have a problem with the blower motor or blower motor resistor or blower motor relay .
Rear Window Defogger Inoperative

Exchange the rear defogger relay with a known good relay from the under hood junction block.
1. Turn the ignition switch to the ON position.
2. Press the rear defogger switch to the ON position.

Does the rear defogger grid warm?
--
Yes Go to Step 2
NO Go to Step 3

2

Replace the faulty relay.
Is the repair complete?
Go to Defogger System Check --

3

1. Use a fused jumper wire in order to backprobe between terminal A4 of underhood junction block connector C3 and ground.
2. Use a test lamp in order to backprobe between terminal C5 of underhood junction block connector C3 and ground.

Does the test lamp light?
--
Go to Step 4
Go to Step 23

4

1. Use a test lamp in order to backprobe between terminal C5 of underhood junction block connector C3 and ground.
2. Press the rear defogger switch to the ON position.

Does the test lamp light?
--
Go to Step 5
Go to Step 14

Switch, fuse or maybe the wiring to the window has come loose or off, happens alot, kits are available at local auto parts stores...
I hope that helps...

if the radio is after market ...disconnect it and verify where the power and ground supplies are delivered..also if plugs are replaced make sure as to use "spark resistor" type plugs

Original equipment rear auto glass is not designed to have the "heating element" removed...these lines are imbedded into the glass during production. If your current rear defogger is not working, you have a few options. You can replace the entire rear glass (very costly), you can add a new aftermarket defogger strip and connect to original equipment wiring...(maybe to many lines for your viewing...or you can add a rear blower motor vent to the rear shelf...(most effective, aftermarket kits are vailable, probably your best choice to address a need for a rear window defogger. Hope this helps.

There is a module that controls the rear window defogger grid . LGM/ EGM Liftgate or endgate module .Receive's message on class 2 serial data network from the HVAC control module to turn it on when button pressed . Fuse # 3 30 amp located in the rear fuse box . Do you know where the rear fuse box is ?
Rear Window Defogger Description and Operation
Rear Window Defogger System Components
The rear window defogger system consist of the following components:
• HVAC control module
• Liftgate module (LGM)/endgate module (EGM)
• Rear window defogger grid
Rear Window Defogger Operation (With LGM)
Battery positive voltage is supplied through the LGM 2 fuse to the LGM for the rear window defogger system. When the rear window defogger switch is depressed, the HVAC control module illuminates the rear window defogger indicator, and sends a class 2 message to the LGM to enable the rear window defogger. The LGM enables the rear window defogger by allowing battery positive voltage to the rear window defogger.
When the rear window defogger switch is pressed for the first time, the defogger cycle lasts 10 minutes. Further operation results in 10 minute defogger cycles.
Rear Window Defogger Operation (With EGM)
Battery positive voltage is supplied through the EGM 2 fuse to the EGM for the rear window defogger system. When the rear window defogger switch is depressed, the HVAC control module illuminates the rear window defogger indicator, and sends a class 2 message to the EGM to enable the rear window defogger. The EGM enables the rear window defogger by allowing battery positive voltage to the rear window defogger.
The following conditions must be met for rear window defogger to operate:
• The end gate glass position is not below the index position.
• The window express down movement is not requested.
• The window down movement is not requested.
If the end-gate glass is not fully closed, the DIC displays "Tailgate Glass Down" when the rear defogger operation is attempted.
When the rear window defogger switch is pressed for the first time, the defogger cycle lasts 10 minutes. Further operation results in 10 minute defogger cycles.

Fuse Block - Rear
Beneath the left rear seat

The rear defogger is fuse #14 (40 Amp fuse) in the underhood fuse box,no other fuses, I have the owners manual. If the fuse checks good test the heater grid of the rear defogger, it is most likely is an open circuit, it can be repaired by the dealer or u..

More than likely something has scratched the film that heats up to do the defrosting, Look to make sure it has both wires attached, and use either a test light (make one out of a 12volt bulb and wire if you do not have one.) See if you have electricity to the wires at the ends. If you do, you have a break in the film. You should be able to see where it is broken or scratched. There is an after market repair kit for this, that is not really expensive.

There are 3 fuses that control the rear defogger, and 1 relay

The fuses are: 10 amp HEATER, 10 amp MIRROR-HEATER; under the dash
The 30 amp DEF fuse is in the fuse box under the hood
The relay is the DEFOGGER relay, which is on the back side of the fuse panel under the dash

Also, check for a loose wire on the defroster grid (on the back glass), this is the most common problem.