Hi Guy's

My rear demister has decided not to work the light comes on on the switch in the centre console but nothing happens. I am aware I can do a couple of test with my multi meter one on the two wires at that attach at to the rear window and on by putting the multimeter pins on each connector end of the glass (this appentley will check the circuit within the glass its self IE any breaks in the conductive wire), could anyone tell me what to look for in both these tests

Also what is the fuse for the rear demister mine is a 1.2 actice 57 plate.

Thanks in advance

Dean

Check the fuse. The fuse number and location will be in your handbook.

If you know how to get access to the two ends of the 'conductive wire', do the following:

1) When the switch is on, check that you have voltage across the two ends of the conductive wire.

2) To test if you have any breaks in the conductive wire, set the multimeter to continuity (as shown in the attached pic) and connect the probes to the two ends of the conductive wire. the multimeter should start beeping. That means that you have continuity (i.e. no breaks in the conductive wire)

Cheers guy's will check these out tonight when i get in and keep you all updated.

Thanks for all your help so far

Hi Guy's

Okay have taken both wires off the window and conected the multimeter as shown and it is showing as being a complete circuit.. so would think it aint the window.

When I have the wires off and connect them directley to the multimeter with the window switched on it shows a reading of just over 12v. But doesn't show on the multimeter as a complete circuit when this is checked nothing happens.

When I connect the wires back the window and check with the multi meter is will only show a reading of 0.28v, but when checked it will show as a full circit.

Any ideas guy's i am know completley baffald.

Thanks in advance.
Dean

my money is on a broken wire in the boot hinge area a partially broken wire will give you 12 volts BUT when under load there will be insufficient conductivity under load

simple check to rule out the ground wire is to attach a lead of thick wire to the 0v (-) rear window terminal (spade crimp or crocodile clip) and secure it to say the rear wheel bolt or other clean bit of metal on the main chassis


i'd pull the rubber boot off the upper left corner of the boot hinge area and have a look see


https://www.fiatforum.com/grande-punto/173223-grrr-rear-screen-wash.html

done the earth check and its the same voltage showing only 0.27 - 0.30v

I have take off that grommet on both sides what so i look out for will the wire be like partialy snaped as i carn't seem to see any breakages.

sorry if i am being a pain just really want it sorted before winter proberly sets in.

Cheers

I have checked the wire in that rubber grommet hinge thing, and there are no breaks at that part.

Is there any other areas there prone to snapping or any other ideas of what else it could be.

or is there any way of checking were the break will be if it is that?

Thanks
Dean

Hi Guy's

Okay a bit of an update,

I have made up and fitted a complete new wiring loom to the rear de-mister uing 35amp wire, have changed the fuse and have also changed the relay the switch is connected to.

Have tested the window and yes it is showing a complete circuit.

And still no de-misting happeneong just the same the wires off the window it shows full votage just over 14v with the engine running and then connect them to the window it shows like 0.28v. :bang:

and yes i have beren up and tested every line on the window by touching the ends of each line with the multi meter and they all show the same voltale 0.28.

Any more udeas guy's would be so appreciated.

Thanks in advance

I too have a non-functioning rear window heater yet the mirrors heat fine. Had a quick look in the dark tonight and couldn't see the wiring connector, is it hidden under the boot trim panel?

Hi yes open the boot look up and inside the little hadle thing there is a screw remover this and the firmley but carfully pull the plastic panal away.

And the connectors are just behind there.

Hi Guy's

I have accepted that there must be a fault in the window some how.

anyway got quoted £400+ by Autoglass then got another quote for £242 of there competitor, But just found a company in manchester a small independant Supply the same brand glass as fiat fully fitted at my front door £145.62 inc vat. thought that was an amazing price.

Being done on saturday so will let you know if this works.

Cheers
Dean

deanm1 said:

Hi Guy's

I have accepted that there must be a fault in the window some how.

anyway got quoted £400+ by Autoglass then got another quote for £242 of there competitor, But just found a company in manchester a small independant Supply the same brand glass as fiat fully fitted at my front door £145.62 inc vat. thought that was an amazing price.

Being done on saturday so will let you know if this works.

Cheers
Dean

Click to expand...

This must bother you more than me, I'd rather just turn the ac on to clear the window. I hope the new window fixes the problem, I just hope mine is a different problem!

Hi Guy's

Okay still not working I have done the following already.

New Window
New Loom
New Fuse
New Relay

This is driving me up the wall now never mind the £200 I have spent so far tring to get to the bottom of the problem.

What else is there left that it could possible be.

Cheers
Dean

Why don't you just smash it? It's £75 with most insurers and has no effect on claims. I did this on a mk2 Punto as I wanted a spoiler, but the fiat one bolts thru the glass, so needed the sporting rear window.

Tried a new boot lock? Is that not wear electrical contacts are?

Already had a new window fitted and new loom fitted,

The boot lock is fine there is no water ingress in the boot atall.

Could it be something simple like the actual switch on dash?

The little light does come on on the switch in the dash and when you switch it on the wires at the back get a full 14v when the engine is running so there is definatley power getting to it.

Its just puzzleing

It works Yeahhhhhhhhh

I didn't relise it run with two relays one that runs the switch inside the car and the other for the power supply.

Anyway its works but it was just a £7.99 relay in the end and i just paid for a new window.

My wife is going mad but hey hoe it works.

cheers