What will cause your speed odometer gages go nuts and your brake lights to stop working?

That's why you don't let you husband work on your car ! Unless he does it for a living .. For MPH there is a VSS - vehicle speed sensor , for the gas there is a sending unit in the fuel tank, for the temp. gauge there is a temp. sensor located in coolant stream on the engine .You more then likely need to have you instrument cluster repaired . GM had a problem with step motors inside the instrument cluster . A step motor is what controls the individual gauge. The sensors are all inputs to the PCM - powertrain control module (engine computer ) .
Engine Coolant Temperature Gage
The IPC displays the engine coolant temperature as determined by the PCM. The IPC receives a class 2 message from the PCM indicating the engine coolant temperature. The engine coolant temperature gage defaults to C or below if:
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The PCM detects a malfunction in the engine coolant temperature sensor circuit.

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The IPC detects a loss of class 2 communications with the PCM.

Fuel Gage
The IPC displays the fuel level as determined by the PCM. The IPC receives a class 2 message from the PCM indicating the fuel level percent. The fuel gage defaults to empty if:
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The PCM detects a malfunction in the fuel level sensor circuit.

?€¢
The IPC detects a loss of class 2 communications with the PCM.

When the fuel level is less than 14% (84ohms), the low fuel indicator illuminates.
Odometer
The IPC contains a season odometer and a trip odometer. Momentarily press the trip select/reset switch in order to toggle between the season odometer and the trip odometer. Press the trip select/reset switch for greater than 1.5 seconds, while the trip odometer is displayed, in order to reset the trip odometer. The IPC displays the vehicle mileage and trip mileage as determined by the IPC. The IPC calculates the mileage based on the vehicle speed information from the PCM. The odometer will display 'error' if an internal IPC memory failure is detected.
PRNDL Display
The IPC displays the selected gear position as determined by the PCM. The IPC receives a class 2 message from the PCM indicating the gear position. The PRNDL display shall flash all gear positions if:
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The PCM detects a malfunction in the transmission range switch circuit.

?€¢
The IPC detects a loss of class 2 communications with the PCM.

Speedometer
The IPC displays the vehicle speed based on the information from the PCM. The PCM converts the data from the vehicle speed sensor to a 4000 pulses per mile signal. The IPC uses the vehicle speed signal circuit from the PCM in order to calculate the vehicle speed. The speedometer defaults to 0 mph (0 kph) if a malfunction in the vehicle speed sensor circuit exists.
Tachometer
The IPC displays the engine speed as determined by the PCM. The IPC receives a class 2 message from the PCM indicating the engine speed. The tachometer will default to 0 rpm if:
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The PCM detects a malfunction in the engine speed sensor circuit.

?€¢
The IPC detects a loss of class 2 communications with the PCM.

Before doing something drastic ,have it checked out for DTC'S - diagnostic trouble codes . It may not be the anti-theft system ,gauges going flat would be more like a communication problem between modules . PCM / BCM / instrument cluster etc.. That also could cause theft light coming on . If your not sure what to look for ,take it to a ASE certified professional . You may render your vehicle useless if you don't know what your doing .
Serial Data Power Mode Master
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle, the PMM is the body control module (BCM). The PMM receives 3 discrete ignition switch signals to differentiate which power mode will be sent over the Serial Data circuits. The 3-wire Ignition Switch table below illustrates the state of these inputs in correspondence to the ignition switch position:
Serial Data Messages The modules that depend exclusively on serial data messages for power modes. stay in the state dictated by the last valid PMM message until they can check for the engine run flag status on the serial data circuits. If the PMM fails, the modules monitor the serial data circuit for the engine run flag serial data. If the engine run flag serial data is True, indicating that the engine is running, the modules fail-safe to RUN. In this state, the modules and their subsystems can support all operator requirements. If the engine run flag serial data is False, indicating that the engine is not running, the modules fail-safe to OFF-AWAKE. In this state, the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.
Indicators and Warning Messages
Refer to Indicator/Warning Message Description and Operation .
Engine Coolant Temperature Gage
The instrument panel cluster (IPC) displays the engine coolant temperature as determined by the powertrain control module (PCM) or the engine control module (ECM). The IPC receives a serial data message from the PCM/ECM indicating the engine coolant temperature. The engine coolant temperature gage defaults to 38?°C (100?°F) if:
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The PCM/ECM detects a malfunction in the engine coolant temperature sensor circuit.

?€¢
The IPC detects a loss of serial data communications from the BCM.

Fuel Gage
The instrument panel cluster (IPC) displays the fuel level as determined by the powertrain control module (PCM) or the engine control module (ECM). The IPC receives a serial data message from the body control module (BCM) indicating the fuel level. The fuel gage defaults to E (empty) if:
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The PCM/ECM detects a malfunction in the fuel level sensor circuit.

?€¢
The IPC detects a loss of serial data communications from the BCM.

When the fuel level is less than 14 percent, the low fuel indicator illuminates.
Odometer
The instrument panel cluster (IPC) contains a season odometer and a trip odometer. Momentarily press the trip/reset switch in order to toggle between the season odometer and the trip odometer. Press the trip/reset switch for greater than 2 seconds, while the trip odometer is displayed, in order to reset the trip odometer. The odometer is calculated and stored electronically in the body control module (BCM). The BCM uses the vehicle speed information from the powertrain control module (PCM) to calculate the odometer. The odometer displays 'error' if an internal IPC memory failure is detected. The IPC stores a backup copy of the odometer value incase the IPC stops receiving a valid odometer value from the BCM.
Speedometer
The instrument panel cluster (IPC) displays the vehicle speed based on the information from the ECM/PCM. The IPC receives the vehicle speed information from the BCM via the serial data circuit. The speedometer defaults to 0 kmh (0 mph) when the following occurs:
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The powertrain control module (PCM) or the engine control module (ECM) detects a malfunction in the vehicle speed sensor circuit.

?€¢
The IPC detects a loss of serial data communication from the BCM.

Tachometer
The instrument panel cluster (IPC) displays the engine speed as determined by the powertrain control module (PCM) or the engine control module (ECM). The IPC receives a serial data message from the body control module (BCM) indicating the engine speed. The tachometer will default to 0 RPM if:
?€¢
The PCM/ECM detects a malfunction in the engine speed sensor circuit.

?€¢
The IPC detects a loss of serial data communication from the BCM.

There isn't any fusible links attached to the fuel pump relay.

If the odometer is analogue then it could be a broken speedo cable!

That's still under warranty, is it not? Take it to the dealer - let the manufacturer pay for the fix.

vehicle speed sensor located on rear output case of transfer case

You need to contact the dealer parts dept or a salvage yard with a cross over reference book for this model and years you have.

I have the same problem developed with my 2002 325i.
Mine would have this problem after about 20 minutes of driving.
Anyone know what is causing this?
Changed ABS sensor, no improvement.

Hi, Autozone will scan your vehicle for free 1997 and newer vehicles. Your brake fluid being low will also make the brake light go on. Ihope this helped you out. Good luck, .....MIKE-

Usually the ABS computer knows what it is doing. You may want someone to hookup a scanner to the ABS test port.
When I had my speedometer and odometer act up, it turned out to be a bad alternator. You might want to check yours.