Rear window demister

[craig2105]

Just back from a little run out, and the rear window has misted up - first time in my ownership! As half expected, the demister doesn't work, so does anyone have any tips on tracing faults on these things? The switch does light up if that helps!

Thanks

 

[DavidL]

Check the boot struts are wired up properly and that they are the right ones.
You can buy aftermarket struts that will hold the hatch up but not do the electrics - ask me how I know [].
The need to be 944 marked parts and they are handed.
Otherwise its chase the electrical fault - we need someone to outline how to use a multimeter properly. I know I'd find it useful.

PS how do you check a relay?

 

[Mike_Pollock]

Craig - i agree with David, check the connections on the struts. you can run wires along struts but probably treat that as temp job.

David - MULTImeter says it all, there are so many ways of using one.
Usually you are looking for a voltage or continuity, on the cars usually 12V (set it to 20V DC) - Black to clean metal og the body, Red to the wire that should be working!
For continuity, ohms scale, basic use dosen't matter which one, best used with car off or bits isolated - 1 = perfect connection 0= broken wire (dud bulb etc.). Can get complicated with bits still on car as current can find its way all round car, making test of component unreliable, unless you know what you're doing (not me!)

Relays - you can listen for them clicking, indication that incoming signal is present. Otherwise you need to remove it and set up test circuit.
There are several "standard" relays and can often be swapped for one on a known good circuit to test.

Hope that helps but Im sure a better explaination will be along soon
Mike

 

[craig2105]

Thanks guys - will check it all in the morning.

And thanks Mike for the multimeter guidance too. Very useful.

 

[DavidL]

Cheers Mike.
Funny I've just spent half an hour reading my newly acquired Haynes electrical manual and it says the same!
One question - if measuring continuity with the multimeter are you utilising the meter itself to supply some sort of current for the meter to measure around your mini test circuit as you would with a powered continuity tester or can you only test continuity by measuring resistance (or the lack of) with said multimeter?
I am having trouble with this resistance idea - you can measure its presence in the absence of any current - ie just with the meter - or again is the meter itself providing the powered circuit to check for resistance in?
I think that all makes sense!
Maybe...

Thanks
David

PS I need to check my ABS relay - now I think I can test it off the car now I've read a bit but as its a 4 pin relay should I have a "general" relay on the car I could replace it with or is it more specific than that?

 

[Mike_Pollock]

Hi David
Yes the meter has an internal batterythat porvides the current for resistance testing,which is why it is better done off the car as there may be "leakage" in situ.
ABS - I know nothing about I'm afraid but a 4 pin relay 1 is earth, 1 is live when operation is reqd,1 permanant live (usually larger wire ) last is live to operate also large wire. but testing is difficult in situ as you cant get to terminals. out of the car you need to make up a circut. not sure if there is a suitable swap available as they operate very quickly and repeatedly so not quite "standard" automotive kit.
Mike

 

[sulzeruk]

Hi Craig, if your struts are the wrong ones, I have a very good second hand genuine set with excellent gas pressure in them, kept the tailgate up no bother,
Al Cowan

 

[Mike_Pollock]

Hi Al
If Craig doesnt want them, can I be next in line ?
Cheers
Mike

 

[sulzeruk]

No probs Mike.

 

[Eldavo]

Hi Al, I can't send you a Pm for some reason so could you send me those pics please.

Ta

 

[JamesO]

With the heated rear window, the small lengths of wire with the crimps to the struts tend to get brittle over the years and breakdown internally. Easy enough to replace though.

 

[944 man]

If the fuse has failed and if replacing it causes it to fail again the Id suspect the rear struts. Wiring them correctly isnt an issue, but theyre sided and fitting anything other thn a left and a right hand part in the correct location will cause the rear window element to short circuit.

 

[craig2105]

All is now well - thanks for the advice everyone. I checked it all over and one of the spade connectors wasn't making good contact on the nearside strut. The struts are fine too so Mike - tap up Al for his spares. Thanks for the offer though.

I love it when it's a simple fix, and with something like a completely obscured rear window, it's great when you can get it to work again because the difference is immediate and gratifying. Am I weird? []

 

[Fat Albert]

I have the same issue, although this morning the mirrors cleared and the hatch got half clear and stopped...I guess I will be breaking out the multimeter at the weekend!