Rear Demister Fuse continually blows (again)

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PeriRollah
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Rear Demister Fuse continually blows (again)

Post by PeriRollah » Tue Dec 22, 2020 1:30 am

Hi All,

I know that this is a subject which has come up time and time again but I'm struggling to get my head around what's happening in my 1995 bongo with manual heating controls. I suspected foul play when I had NO demister button but did find the 4 pin female plug lurking behind the dashboard . I bought a button from a breaker that blew the fuse even as soon as I pressed it !!!! The button did not appear to click in and click out, so think that this button is also faulty (I hopefully have another one coming tomorrow)

3d4b7553-1ccd-49af-baad-2cad46e1d147.jpg
WIth a new 30AMP fuse in place but with NO switch now, I see 12 volts at the white thick wire. The thick black and yellow cable, the thinner red and thinner black wire (not in view) all appear to have continuity to ground which is confusing me. I am assuming that the black and yellow cable becomes live once the switch is pressed and the remaining thinner pair of wires to illuminate the switch when pressed.

The wires in the tailgate hinge were damaged and were resoldered
39a22c0d-cee3-431f-a9b9-646efb578c6d.jpg
BUT the black and yellow wire here, is part of a two pin plug along with a plain black wire . With this two pin plug disconected from the tailgate I still see continuity between the terminals on both the powerside and tailgate side of the plugs.
9b5f89a0-e00d-4bb2-88de-69ee890a59e3.jpg

I'm just wondering if anyone has investigated this particular circuit here as wondering if I do have a short somewhere. I wouldnt expect the black and yellow wire (which I assumed was the live power) to have continuity to ground on the powerside of the plug whilst disconnected from the tailgate. I have removed both trim panels on the drivers side and tapped into the both B&Y and the black wires between c and d pillar and by the rear heating controls before the loom disppears under the floor towards the front of the bongo. They both have continuity between eachother /ground

I am currently unable to compare with a working vehicle at the moment hence my post here.

I have looked at the wiring diagram http://www.g8dhe.net/bwm/bwmanualp.htm?1997/Page_94 but this looks like the diagram for bongos with digital climate and a demister button that has the 10 minute timer?

I was wondering if there was a diagram for early bongos with manually controlled heaterf settings and/or anyone familiar with this subject could please help?

THanks for your time,

Regards

Dek
PeriRollah
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Re: Rear Demister Fuse continually blows (again)

Post by PeriRollah » Tue Dec 22, 2020 2:10 am

Found this page also for 1995 cars

http://www.g8dhe.net/bwm/bwmanualp.htm?1995/Page_96
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g8dhe
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Re: Rear Demister Fuse continually blows (again)

Post by g8dhe » Tue Dec 22, 2020 10:33 am

Well you have found the diagram, which gives all the info you should need. The switch causes the relay I1-01 to operate, this than connects the heater element via the fuse to the 12 volt supply and also to the indication light in the switch. If the 30 Amp fuse blows each time the switch and hence relay operate it would suggest that the Black/Yellow wire is shorting to earth somewhere along its length, possibly where the repair to the broken wire was carried out in the loom between chassis and tailgate or possibly the connection to the indicator light on the switch.
Geoff
2001 Aero V6, AFT, full side conversion.
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PeriRollah
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Re: Rear Demister Fuse continually blows (again)

Post by PeriRollah » Tue Dec 22, 2020 10:59 am

Hmm yes it should do. To clarify, that page for 1995 models; is this showing circuits for models with both digital climate (which uses relay/switch I1-01) and manual where there is just the dashboard 4 pin switch I1-02 on the right side?

Looking at the colour cables into that 4 pin plug under the dash , it is black , red/blk, blk/yellow and white/blue which relates to I1-02

The loom looks pretty sound from the moment it comes up into the cabin behind the drivers seat, they're not unwrapped/disturbed right up to the plug, which I've disconnected, below the right rear window below between C and D pillar (before it disappears behind offside lights and out of the body by the hinge)

I'll try and isolate the blk and yellow wire but it seems connected to earth both with no switch and unplugged between C and D pillar , maybe the issue is between the under dash plug and where it disappears under the floor. I'll keep looking.

Thanks again
Last edited by PeriRollah on Tue Dec 22, 2020 11:40 am, edited 1 time in total.
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g8dhe
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Re: Rear Demister Fuse continually blows (again)

Post by g8dhe » Tue Dec 22, 2020 11:23 am

Yes as far as I am aware, its the same for all versions and years I normally refer to the 1997 version as the text is in Roman rather than Kanjii and the colour codes via the lookup table on the status line are easier to work out ;-)
Geoff
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PeriRollah
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Re: Rear Demister Fuse continually blows (again)

Post by PeriRollah » Tue Dec 22, 2020 11:43 am

OK I edited my previous post to add more detail but it looks like the 1995 manual are for cars between may 1995 and october 1997, the circuits are different. But yes the symbols are :shock: to work out even zoomed in :-)
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