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It can get a scratch that goes thro' all the elements.
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>>i've used a voltmeter
Ah, beware! The voltmeter draws a negligible current unlike the heated rear screen. So, if there's a poor connection with high resistance anywhere in the circuit, your voltmeter may not find it, because the resistance of your voltmeter is still many times higher than the resistance of the bad connection. Voltmeters can, and frequenctly do mislead people when there's a poor connection, and it's sometimes better on power circuits like the HRW to use a tester which draws more current, like a 21W bulb.
However, staying with the multimeter, the best voltmeter check to make is with all the connections in place and the HRW switched on (does the engine need to be running too to activate the relay?), measure the voltage across the heated rear window - I suspect it will be close to 0v.
To find where the bad connection is, live side or earth side,
1) put the positive lead of your multimeter to a known live terminal (ideally on the battery, you may need to run a length of wire temporairly), and the negative side to the positive connection of the switched on heated rear window. The voltage drop should be small - less than 0.5 v ideally.
2) put the positive lead of your multimeter on the eart connection of the switched on heated rear window, and the negative to a part of the body that's been scratched back to clean metal (i.e., a known good earth). Again, the voltage drop should be small.
Whichever of 1) or 2) which shows a large voltage drop indicates which side of the circuit needs more investigation.
If the positive side is suspect, you can then isolate where the fault is by moving the positive multimeter connection along the circuit. When the result changes, you've just passed over the dodgy component / connection.
Number_Cruncher
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thanks numbercruncher and everyone else for your comprehensive replies. i,ve tried maplins there circuit repair paint [brush on] is out of stock they have the same stu ff in a pen like dispenser but it's £21.i've had another look at the r.h.s and the top line of the element actually works [checked by breathing on it] my pals suggested trying some self adhesive copper strip he's got its about 3mm wide and 5thou thick if i can cut it narrow enough. but first i,ll try the 21watt test lamp in case there is a dodgy connection and it,s only able to power 1 line of the element.
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Although it's possible, do you think that all of the elements are damaged? I think it's unlikely!
I seriously doubt whether it's the elements at fault.
Using your multimeter to find where the voltage drop is would be my next move.
Number_Cruncher
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It is possible to ruin a whole screen by cleaning it with aggressive solvents - if one element is working maybe that's what's happened?
With the wires [carefully] disconnected; what's the resistance across the screen between the tags?
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i think the previous owner had some transfers etc stuck on the inside of the rear screen across some of the elements that may have damaged the elements when they were removed.theres evidence of it when the screen mists up, you can see the outline of stickers that had been there. let this be a word of warning!
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I wonder if someone used glue remover or brake cleaner to clean off the residue from the stickers?
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>>and the top line of the element actually works
Ah, sorry!, I missed that.
Number_Cruncher
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With the screen fully disconected, measure the resistance across it, it should be very low, certainly below 5 ohms.
Then to find which lines are or aren't working, measure the resistance between one connector and the furthest end of each individual line, again there should be very low resistance, any fault usually shows itself as a higher resistance than the lines above and below (bearing in mind there may be a slight difference between lines as their lenghts vary.
Is it possible that the car had tints on it in a previous life? if a numpty has removed said tints with a blade, they could well have damaged all but the one working line?!?
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Would it be worth trying to source a new or used back screen from a scrappie....?
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My son in laws mother used to carry a hoover around in the back of her hatchback when she shut the tailgate the heater elements were rubbed away by the corragated hoover hose.She ended up with no rear heater.
--
rustbucket (the original)
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