Granville Heated Rear Window Repair

Halford's reviews:

When Halfords eventually managed to supply the stuff (at the third attempt, 'Click and Collect' being more like 'Click and We Can't Find It' the first two times, but they did knock a bit more off for my trouble) I checked the consistency at the counter and that was fine.

However shaking didn't do anything for mine as it's too gloopy, it did eventually move to the other end of the bottle when I left it upside-down on the desk for a while, and to be sure I stirred it with a straightened-out paper-clip.

Finding the break is another departure from above. It may be down to the multi-meter you use but the continuity buzzer on mine did nothing, even when the two probes were positioned right next to each other on a working track. There is also the difficulty of keeping two probes on what is the very narrow tracks of OEM HRWs, the older after-market stick-on ones that were around in the 70s may be easier as they were quite bit wider. I found it much easier to power it up, then with the meter on volts and the negative terminal clipped to an earth point nearby, you only have one probe to worry about. When you are on the live side of the break you will see full system voltage, and when you are on the earth side of the break it will drop immediately to 0v. If you test a working track you will get at gradual reduction in voltage as you move along the track from the 12v side to the earth side, being about 7v in the middle when the engine is running (as the ZS has to be before the HRW can be turned on). I could not see any break in the track, even with a magnifying glass.

A warning about your meter probes, make sure you use something with a rounded tip with no sharp edges, or you may make more breaks in the track.

I didn't even try the included mask, the slot is much wider than the tracks, and probably more applicable to the after-market stick-on types from the 70s. It's quite tricky getting the edge of the masking tape up against the edge of the track, both top and bottom, especially on a 4-door with a 'parcel shelf' under the sloping glass. Easier to see when you have got it right from the outside. I found the location first, then stuck a short length of masking tape above and below the track either side of the break, then marked that with a pencil at the exact point of the break i.e. where the voltage transitioned from 12v to 0v. In fact the edges of the tape acted as a guide for the probe, I just had to gently slide the probe along, the edges of the tape keeping it on the track.

A further departure was shortly after applying the first coat I gently peeled one end of each strip of masking tape back a little just past the break. As some of the liquid was inevitably on the tape, I was concerned that only peeling the tape back after leaving it for 20 minutes for the first coat to dry and then applying the second coat, the tape would peel both coats off the very narrow track. I completely removed the tape just after applying the second coat, then left it alone overnight.

Next time the screen needed clearing it was obviously the repair hadn't worked, and testing showed the voltage changing right at the end of the repair. I'd carefully marked on the tape where the voltage changed before, so that was odd. Next sunny dry day I had another go, extending the bead. As the sun was shining directly on the screen I thought perhaps it wasn't a good idea as it would be in my eyes, but in fact I could see two or three 'pin-holes' in the track just past the repair, on the side that the voltage changed, and none elsewhere. Perhaps a weak section that had always been there, so I made sure the new bead covered them all, and now wait to test it again.

Still didn't work, and annoyingly a year later another track has failed!