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Backup Fuse Keeps Blowing in 2006 Legacy


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Hi, new member here wondering if anyone can help with an electrical issue in a 2006 Legacy. My backup fuse under the hood keeps blowing - this is the 20A fuse for the constant power circuit, supplying things like the clock, interior lights, etc. Without it the climate control and audio system don't work either. 

I've just pulled every fuse out of both boxes with the idea of plugging them in one-by-one until the backup blows, then I'd know what was causing it. But even with all of the fuses out the backup fuse blows as soon as it's inserted. So the question is what is connected to the backup fuse that doesn't have it's own fuse in either box? The alarm? 

Thanks in advance! 

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Wagon?

IIRC, the backup lights on that are in the hatch. The wiring harness that passes from the body into the rear hatch is pretty notorious from breaking with the fatigue from opening and closing the hatch causing all kind of electrical gremlins. It is absolutely possible to splice in a new section of wire, but the most complete fix is to replace that whole harness. We kept them in stock at the dealer where I worked, and MSRP was about $80.

Pull the back edge of the headliner down, and unplug that harness from the body, and then see if your fuse blows.

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Thanks, yes waggon. Would that still cause the backup fuse to blow though when the backup light's fuse is removed? As I said, I pulled all of the fuses out of both boxes (with the exception of the airbag fuse), but even then the backup still blew the moment it was inserted. 

Edited by Ed209
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I kind of doubt it is the rear hatch wire, but anything is possible. The Harness shows the rear room light exits the harness a few inches before going into the rubber tube.

Is the fuse circled in the picture the one you are replacing?

Fuse No.8 20-AMP
This fuse supplys these 3 distrabution points. FB-10 FB-11 MB-29.

FB-10 
Audio
Keyless entry control module
Step light LH
Step light RH
Clock
TV monitor

FB-11 
Trunk room light (Sedan model)
Navigation control module
Luggage room light (Wagon model)


MB-29
Auto A/C control module
Spot map light
Body integrated unit
Home link
Room light

I looked at most of the items listed and did not see a second fuse going to them, so any of them or their wire would blow that fuse.

Each one of those Items would have to be disconnected or unpluged to see if it is the problem. If the fuse still blows, then it would have to be at least one of those wires shorted to body ground or shorted to another wire somewhere in the harness.

The FSM has the wiring diagram and also the Wiring Harness and Plug numbers and where they are located in the vehicle.

Also look for any kind of damage to the wiring harness. Example-the harness that goes to the rear room light and tail lights is routed behind the side panels. Not fun.

You can download the Factory Service Manual at either of these sites.(I donated to both)
http://jdmfsm.info/Auto/Japan/Subaru/

On this link, make your selection and when you click the Download button a second page will open, it's an add, click the X to close it.
https://sl-i.net/FORUM/showthread.php?18087-Subaru-Factory-Service-Manuals-

Hope this helps.

Main Fuse Box.jpg

Edited by Rampage
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On 3/6/2020 at 5:07 PM, Ed209 said:

Sorry, should add that the fuse is labelled backup, but it protects the constant power circuit (not the backup lights). 

Ah, I didn't follow that. Not much I can tell you remotely. I'd be printing out all the diagrams for everything on that circuit and working my way through it with a multimeter

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