Rear Screen Demister

For all electrical questions; Alternators including fitment; Light connections/wiring; Instruments; Gauges; MFA; Heater blower (not coolant related) issues etc etc.
Forum rules
Hints, tips and guides for repair and modification - the FAQ section on the main website is worth checking first for information relating to common faults and technical help. Useful posts and guides will be added to the FAQ http://www.sciroccoregister.co.uk/scirocco-faq
Post Reply
RussGLAuto
Posts: 357
Joined: Sat Jul 14, 2018 11:51 pm
fill in the right answer: 15
Location: Bourne

Rear Screen Demister

Post by RussGLAuto »

Evening gents,

On these cold misty mornings, one thing that has eluded my otherwise gremlin free electrical system is the rear screen demister.

I have replaced the switch, the little light even comes on in the switch is on, so it's getting power. All connections seems sound (!) and I can't find any fuse related item to check on the fuse box. Odd...

Looking at all the window tracks, well, they seem to be in unbroken order, no obvious scratches through them that would cut the circuit.

Any ideas on what to check please?

Cheers

Russ


Daily Driver - 2017 Volvo XC90 T8 Twin Engine - Polestar - Arctic White
Weekend Wagon - 51k 1982 Mk2 Scirocco 1.6 GL Auto - Diamond Silver
Other Half's Wagon - 2018 Mk7.5 Golf GT TSi Auto - White
Daughters Curb Scraper - 2016 Fiat 500 1.2 - White
User avatar
GT_II
Posts: 522
Joined: Thu Feb 23, 2017 11:18 pm
fill in the right answer: 15
Location: Warwickshire

Re: Rear Screen Demister

Post by GT_II »

Broken wires where they pass through to the tailgate? Do you have a working rear wiper? If so, the fault is likely in the live feed to the heater. Otherwise it could be a broken earth wire.


1992 VW Scirocco GT II 1.8 90PS Brilliant Black 30k
RussGLAuto
Posts: 357
Joined: Sat Jul 14, 2018 11:51 pm
fill in the right answer: 15
Location: Bourne

Re: Rear Screen Demister

Post by RussGLAuto »

Yes, the rear wash wipe is working fine.

I'll check if I'm getting power at the window element end, better get myself a multimeter!

If it is the element I guess I'm stuffed?


Daily Driver - 2017 Volvo XC90 T8 Twin Engine - Polestar - Arctic White
Weekend Wagon - 51k 1982 Mk2 Scirocco 1.6 GL Auto - Diamond Silver
Other Half's Wagon - 2018 Mk7.5 Golf GT TSi Auto - White
Daughters Curb Scraper - 2016 Fiat 500 1.2 - White
mark1gls
Posts: 3954
Joined: Thu Apr 02, 2009 9:28 pm
fill in the right answer: 10
Location: Somerset

Re: Rear Screen Demister

Post by mark1gls »

9 times out of 10 it’s a broken wire from where the boot lifts up and down.


Mk1 78 Scirocco GLS 1.6 FR, weekend toy.
Mk1 88 Golf GTi cabriolet 1.8 DX. Daily drive.
Membership No. 323
RussGLAuto
Posts: 357
Joined: Sat Jul 14, 2018 11:51 pm
fill in the right answer: 15
Location: Bourne

Re: Rear Screen Demister

Post by RussGLAuto »

Many thanks, I'll check that too.


Daily Driver - 2017 Volvo XC90 T8 Twin Engine - Polestar - Arctic White
Weekend Wagon - 51k 1982 Mk2 Scirocco 1.6 GL Auto - Diamond Silver
Other Half's Wagon - 2018 Mk7.5 Golf GT TSi Auto - White
Daughters Curb Scraper - 2016 Fiat 500 1.2 - White
RussGLAuto
Posts: 357
Joined: Sat Jul 14, 2018 11:51 pm
fill in the right answer: 15
Location: Bourne

Re: Rear Screen Demister

Post by RussGLAuto »

Evening gents,

So got myself one of those new multimeters for dummies. It shows power getting to and from the rear demister.

https://www.amazon.co.uk/gp/product/B07 ... UTF8&psc=1

I have seen some rear doors for sale stating that several of the 'tracks' are not working so theoretically some at least should be.

Meh... :dash:

Any thoughts...

I did find a new old stock wiring loom for sale on DE Ebay but the chap refused to post it to UK....


Daily Driver - 2017 Volvo XC90 T8 Twin Engine - Polestar - Arctic White
Weekend Wagon - 51k 1982 Mk2 Scirocco 1.6 GL Auto - Diamond Silver
Other Half's Wagon - 2018 Mk7.5 Golf GT TSi Auto - White
Daughters Curb Scraper - 2016 Fiat 500 1.2 - White
User avatar
GT_II
Posts: 522
Joined: Thu Feb 23, 2017 11:18 pm
fill in the right answer: 15
Location: Warwickshire

Re: Rear Screen Demister

Post by GT_II »

When you say power getting to and from the demister, do you mean 12v on one side and zero at the other?


1992 VW Scirocco GT II 1.8 90PS Brilliant Black 30k
RussGLAuto
Posts: 357
Joined: Sat Jul 14, 2018 11:51 pm
fill in the right answer: 15
Location: Bourne

Re: Rear Screen Demister

Post by RussGLAuto »

Good question!

Will have a re-check. The gizmo has a circuit checker on it too, so I know power can get from one side of the window to t'other.

I'll have to get the manual out again. Wish I'd paid more attention in Physics class's instead of playing conkers and chasing girls!!! :laugh:


Daily Driver - 2017 Volvo XC90 T8 Twin Engine - Polestar - Arctic White
Weekend Wagon - 51k 1982 Mk2 Scirocco 1.6 GL Auto - Diamond Silver
Other Half's Wagon - 2018 Mk7.5 Golf GT TSi Auto - White
Daughters Curb Scraper - 2016 Fiat 500 1.2 - White
User avatar
GT_II
Posts: 522
Joined: Thu Feb 23, 2017 11:18 pm
fill in the right answer: 15
Location: Warwickshire

Re: Rear Screen Demister

Post by GT_II »

So it sound as though at least some of the heater wires are good. The next step in the diagnosis would be to measure the voltage between each end of the heater and an earthing point. You will find an earthing point somewhere in the luggage compartment, likely under the mat.

With the ignition and heater switched on, you should get a reading close to 12V at one side, and close to zero at the other side. If you get 12V at both sides, that tells you have a bad earth connection. If you get zero at both sides, that means power is not reaching the heater from the switch.


1992 VW Scirocco GT II 1.8 90PS Brilliant Black 30k
RussGLAuto
Posts: 357
Joined: Sat Jul 14, 2018 11:51 pm
fill in the right answer: 15
Location: Bourne

Re: Rear Screen Demister

Post by RussGLAuto »

I think you may have just struck gold. I didn't have anything turned on when I was poking around!

Duh...


Daily Driver - 2017 Volvo XC90 T8 Twin Engine - Polestar - Arctic White
Weekend Wagon - 51k 1982 Mk2 Scirocco 1.6 GL Auto - Diamond Silver
Other Half's Wagon - 2018 Mk7.5 Golf GT TSi Auto - White
Daughters Curb Scraper - 2016 Fiat 500 1.2 - White
User avatar
GT_II
Posts: 522
Joined: Thu Feb 23, 2017 11:18 pm
fill in the right answer: 15
Location: Warwickshire

Re: Rear Screen Demister

Post by GT_II »

Rule of thumb. If you're checking resistance or continuity through a circuit, you need the circuit switched off, with one probe at each end of the circuit (usually doesn't matter which way). If you're measuring voltage, you need the circuit switched on, with one probe (+ve) on the point in the circuit you are testing and the other probe (-ve) connected to earth (car body). And obviously with the meter set to DC volts not AC.


1992 VW Scirocco GT II 1.8 90PS Brilliant Black 30k
Post Reply