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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old November 10th, 2002, 21:59   #1
volks27
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Location: Gatineau, Quebec
Default Rear Defroster switch blows fuses... HELP

When I press on the rear defrost button, it blows out my 20A fuse in the fusebox.

I unhooked the rear defrost at the window and still does it.

I unhooked both side-rear view mirrors and it's not blowing fuses anymore. Anyone has an idea? Maybe one of those elements is toast??

Can anyone help, its a 99.5 Golf Mk4, has defrost option in the side mirror, controled my the main switch (not by the joystick in the driver's door like newer golfs)

Thanks
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Old November 10th, 2002, 23:25   #2
rwolff
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Default Re: Rear Defroster switch blows fuses... HELP

Where did you unhook the wiring to the mirror heaters (at the mirror, or close to the switch)?

Heating elements tend to fail "open" (there have been other posts here about how an old heated mirror had a much higher resistance than its replacement), but the wiring from the switch to the mirror passes through a flex section (to allow the door to open).

I'm assuming you unhooked the wiring close to the switch. If there's a bad grommet, or for some other reason the wire chafes against a panel edge (either with door opening/closing or with vibration on the road), the insulation will wear through and put the wire in contact with the body (i.e. ground). Get an ohmmeter and check the resistance to ground for each of the mirrors at the connector you unhooked - my bet is that one (or both) has its wire shorted to ground before it even reaches the mirror.
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Old November 11th, 2002, 04:58   #3
volks27
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Default Re: Rear Defroster switch blows fuses... HELP

I unhooked the wiring at the mirror itself, not at the switch

If I do a ohm check on the wiring while it's unplugged, across the pair at the mirror, I get 10K (If I had a short, it would be under 1K)

I did check the resistance of the (unhooked)elements, they are both 5-10 ohms...

Also, I'm running the rear defrost now and the fuse is not blowing so it's probably not a wiring problem.

The rear window's resistance is over 8 meg-ohms

i'm confused now [img]images/icons/confused.gif[/img]
PS: I did study electronics 3 years so any suggestions, pass it on! Thanks
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Old November 11th, 2002, 07:54   #4
Snowman
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Default Re: Rear Defroster switch blows fuses... HELP

Well, it's conquer and divide time. I haven't looked at the switch on mine so I'm just guessing. I don't know if it's a DPDT or SPDT switch, but I'd be also checking the switch itself for shorts when activated.
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Old November 11th, 2002, 08:09   #5
volks27
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Default Re: Rear Defroster switch blows fuses... HELP

I'm getting close to finding this out

All things were working well *until* I opened the hatch on the golf

Then the fuse blew. ugh. I would imagine the hot wire to the rear defrost is touching the body somewhere near the hatch grommet... Time to do the wiggle test! Anyone ever re-routed OEM cable from the dash to the rear?
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Old November 11th, 2002, 10:24   #6
volks27
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Default Re: Rear Defroster switch blows fuses... HELP

okay... This is turing into a cat and mouse game...

I found that there is a short at the fusebox....... ugh

I did a continuity test between ground and the heater fuse and voila... there is ground. If I wiggle the box, it goes away.

Can anyone confirm that there should not be ground at that fuse? In other words: is the defrost circuit fused at the power side or at the ground side? If it's at the ground side, I guess it's ok if I saw ground there... If not I might try re-routing the wire, or finding another fuse location.

[ November 11, 2002, 10:25: Message edited by: volks27 ]
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Old November 11th, 2002, 15:13   #7
MOGolf
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Default Re: Rear Defroster switch blows fuses... HELP

Fuse is on the power side, before the switch. Wiring connection #6 at the switch goes to the rear window grid. #5 is the hot lead from the fuse (#26).
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Old November 11th, 2002, 18:57   #8
volks27
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Default Re: Rear Defroster switch blows fuses... HELP

I think I got it this time

I ran a different cable from the X75 junction (under fusebox) to a external fuse, then to the switch. It seems to work now.... I'll check again tomorrow

Does 15 amp sound resonable for the rear grid (defrost) when on (without side mirror defrost)?

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