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MG MGB Technical - Heated Rear Window

I finally took out the tailgate glass on my GT, there was a slight leak somewhere and I had eliminated all other causes for the HRW not working.
I suspect the leak was simply cause by a PO reusing the seal several years ago after a respray/rebuild.
However it looks like the HRW is completely gubbed (it has never worked in my ownership)
I have power to both sides of the window strips but no continuity across all the elements.
Quite surprised at this, basically all the elements are open circuit but looking at them with a magnifying glass none of them seem broken ( I would probably have repainted any tiny cracks if found)
Is this normal, have never came across a defective one before and certainly one every element is defective.
looking at £160 or more for a new glass, I had been hoping for a bad connection somewhere!
Neckieman

Can you check resistance at several points along the circuit with a pointed probe?
Mike
Mike Ellsmore

Common problem see:

https://octarine-services.co.uk/forum/book.php?id=451

hope that helps.
Chris at Octarine Services

Chris's method is the only and simplest way to check them

Checking by measuring resistance doesn't really work as all the strips are connected together at each end making it impossible to measure the resistance of a single run

Also make sure you have 12v on one side and check to make sure you have a good earth on the other--It's easy to assume the earth is good, but is it-!!--
William Revit

I have the windscreen fully out as I had a slight leak anyway and I wanted to replace the rubber.
I am getting no continuity between the two sides of the window at all, I thought at least some of the lines would be working.
Anyway I have given up on the window, all my tests just show nothing across the window at all, no voltage, no continuity and no current draw.
I have managed to get a new window for £129 from one of my local windscreen shops which I pick up wednesday.
This will go in with a new set of rubbers, when I took the window out I found there had been a long term leak along the bottom which had started corrosion on the mounting flange and had obviously been running into the door. I'll treat this and remount the glass.
I have sorted out the switching and and missing warning light so all should be well once done.
its never worked in the two years I have had the car, it'll be nice to be able to see out the back window!
Neckieman

i tried repairing mine with the conductive paint. spent ages masking to get a nice clean line but still didn't work. now the window looks a real mess as from the outside you can easily see the new paint vs old element.

i have found a retro stick-on (sucker) heater on ebay which works ...just about...but replacement eventually with respray is the plan

G

Graham Moore

I have a brand new HRW in the garage, although one of the spade terminals has become detached.

It may be possible to re-attach it, perhaps with some silver-loaded epoxy, for example, if anyone would like to give it a try?
Dave O'Neill 2

If you had been closer I would have had a go, I am a whiz with soldering and have all sotrs of ways of reattaching things even where temperatures are an issue, even have a resistance soldering unit which is great for delicate items.
However its a pity, it would cost more to come and get it than it will cost me for the new one!
Neckieman

Any other takers?
Dave O'Neill 2

If you have no continuity between the two sides (where did you test?) then the implication is that at least one of the connections down to the vertical strips that feed all the horizontal strips is broken, as it would be very unlikely to have all the horizontal strips broken. However if it has never worked in your ownership then a PO may have damaged all of them with careless cleaning or loading.

My 2004 ZS developed a dead strip, and measuring voltage along the strip with it powered is the way to go. I found the point at which it changed between 0v and 12v (ideally, probably less if all the other strips are working), carefully masked each side of the strip and painted some Granville Electro Connector (supposed to be for HRWs) about 1/4" each side. Left it a couple of days and found it wasn't connected to either side. Extended the strip and it still wasn't connected. Now a second strip has failed.

Incidentally the V8 HRW has always worked but measuring at the screen I only had 7v with the vast majority of the lost voltage in the 12v supply. Fitted a relay in the engine compartment which increased it to 10v, and noticeably better clearing. I know some have mounted the relay in the rear, with a fused connection directly off the battery, and boosted it further.
paulh4

I have the screen removed and measured off the strip down each side. Tried it straight from a battery where I got 12v across the window but nothing along the strips.
Basically its completely gubbed and I don't know the history.
I have a brand new screen I am picking up tomorrow for £129 from one of my local windscreen suppliers, this will go in the car and hopefully should have a working HRW
Neckieman

This thread was discussed between 26/01/2018 and 02/02/2018

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