Rear defrost won't turn off.

Dear Deseree,
I would like to suggest you are on the right track.
Next, try to find the fuse for the rear defroster, and try pulling that. That light may be a lit because of the "instruments" fuse, and if you pull that one, your instruments may stop working.
Fuses are both under the dashboard and also in a black plastic box under the hood of the car near a fender.
I might suggest there are 3 more common things that can cause the battery to drain.
1) a short in the alternator can cause this problem.
2) a short in the ignition switch, and
3) a short in the computer itself.
God bless your efforts.

The rear defro does not have power going to it with the key off. This means there is somehow a short to power to this switch, if you can remove the switch check for power at the connection. If there is power there is a short, I will send you a schematic of the circuit.

You definatly have water inside the car. Pull the carpet back in the front and rear checking for water leaks. The only way frost can develope inside a vehicle is the presents of moisture.
The other possibility is your HVAC drain is plugged and water has built up inside the heater motor area. Have the drain checked and cleaned.

Hello, the short way to check out one possibility is to go to Autozone or Oreillys and ask for a Diode test on the Alternator. This is an internal part that stops the Alternator from allowing the Battery to ground out inside the Alternator.

The next tests will take more time and a Multimeter. It will help to have a helper. You need to disconnect the Battery and hook up the Multimeter to the ends of the battery cables. With every switch shut off only the clock and onboard computer will make contact.

With a multimeter you can measure to total amount of Ohms used. Then try to eliminate the Ohms. Pull a fuse to windows, seats, doors, rear window defroster etc. while keeping a map of where the fuses came from. Once you see the Ohms drop, you will need to find out why that circuit is grounding when it is shut off.

If you take a few minutes to stand by your car, sometimes the Air suspension will run down a battery if the air is leaking out of the system. If you hear the Air compressor running several times then most likely the drain is because of it.

You do not say what brand and model vehicle you have.

The rear window demisters drain a lot of power and are usually programmed to switch off automatically after about 15 or 20 minutes of use. They should also cut out fully when the vehicle's ignition is turned off and of course when you manually switch them off.

1. When you are driving and running a host of electrical units simultaneously in winter there is maximum power drainage and any shortfall in power from the alternator has to be drawn from the battery. This will be a problem if you have a weak battery that is not holding it's charge well or if the battery is not fully charged once it has been nearly or fully drained. It will also be a problem if the alternator is not producing it's optimum power while the vehicle is running.

Batteries do not respond well to being drained frequently and when they are they should always be fully charged again each time with a battery charger at the earliest opportunity. (Running them down and then expecting the vehicle's alternator to do all the battery recharging is not a sound practice).

2. It is possible the rear demister is not shutting down automatically after a period of operation as it is likely to be programmed to do in your vehicle. This is easily checked. If it is not shutting down, and the battery is needed to supplement the vehicles power supply when driving, then the battery can be run down in time.

3. If the rear demister is left active but not shutting down when your ignition is turned off your battery will quickly drain.
You should check that power to the rear demister is off once the ignition is switched off (and when you switch the demister off manually). This is unlikely to be a problem but in the unlikely event that you find it is still operating then you can pull the fuse dedicated to the rear demister.

I 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

I'm guessing the blower motor relay is stuck on, the relay are usually in or near the fuse box. Sometime those relays can get so hot they weld the contacts together. I would suggest disconnecting the battery when you are not using the vehicle, until you can get it to a shop to get it fixed. The vehicle could very possibly start on fire so make sure you don't park it in your garage with the battery connected.

You have a cross short in the grid on the rear windsheild most likley. You can find it with an ohm meter and repair it. For now i would just pull my fuse for the defroster and not worry about it unless there are other components on that circuit that you would like to operate.

pull key out of ignition and wait 2 minutes for the can system to go to sleep(instrument cluster is off) and all doors are shut-no consumers on should be approx. 50 ma.

Check the rear interior light is not continually on in the boot/trunk. Also check the glove compartment light is also not on even when the lid is shut as they warp and allow the switch to stay on. And finally, sit in the car and close the doors. Look at the red markers which are on the end of the doors. At night, you will see these and they should go off. If they don't, then one of your door switches in the lock mechanism is faulty. Has been known for the alarm units to go faulty and draw excess current too. If it is none of these, then stick an ammeter on the battery and pull the fuses one by one until the current draw is reduced. The batteries on these cars only last 3 years before they should be replaced too. It might even be just a dead battery.