Hi, me again! :)

This place seems like a fountain of knowledge! :)

My rear demister doesn't work so well. Specifically, little patches of it work, so when it's foggy I get a few spots that I can see through. The grid lines are all there and at a glance they seem to be continuous (there are no visible breaks). However, on testing it with a continuity tester, I found that looks can be deceiving! I think it was only the top grid line that actually worked the entire way across the window. The remaining lines were broken.

Now, this whole thing doesn't really make sense to me, because surely if a grid line is broken at some point, the entire line shouldn't work, as the circuit is broken?

Anyway I bought a "rear window demister repair kit" which is a tiny bottle of some special metallic paint, and set to work repairing the first broken line. After repairing the first break that I found, I tested again, and basically it turns out that I probably have to paint over each entire grid line, which is very, very tedious, not to mention expensive as the bottles contain 1.4ml of paint and cost about AU$15 each. I think that most of the grid lines have been scratched so much that they don't really conduct anymore, although they look like they're fine.

What options do I have? Would fitting a new rear window with grid lines that work be a viable solution, or would that just be a waste of time and money? I've seen rear demister kits that you're supposed to stick on to the window, but I don't know if I want to use one of those - they seem quite ugly. It looked like you had to stick a large piece of sticky plastic over the entire window, and I don't imagine it would look particularly attractive, even if all the air bubbles were smoothed out!

Thanks again for any suggestions! I think I'll go introduce myself on the "Introductions" forum now!

-Sam

Not sure if it's avail in Aus or not, but in Canada we can get conductive paint that can be used to touch up small breaks in the lines. If you examine the line very carefully, there will probably be a crack in it. Haven't done this for a long time, but if you GENTLY!! trace along the line with a voltmeter, you should see battery voltage right up to the line, then zero at the break.If you do the same on a working line, there will be a gradual decrease to zero.
I have a '67 123GT myself, but we had a yellow 73 144 at one time and my wife never forgave me for selling it. Now she has an '89 240 so I'm out of the dog house.

The rear window out of a 240 will also fit, and of course are newer.

Regards


Pete

No solutions, just commiseration. My 71 1800E rear window has the same problem. It had a fancy two level demister - left side is split into a top half and a bottom half each with their own wire - the right side has a single wire for all the wires. At the 1/2 setting current goes in the top left half, the right side wire is disconnected, so the current goes back over to the bottom left which is grounded (double the length, 1/2 the current flow). And on full both left wires are hot and ground through the right wire.

Fancy indeed - but no current at all flows through the grid. I think years of washing with window cleaner by the P.O. leached out all the metal - leaving just a non-conducting remnant behind.

My guess would be a new window is the best bet. If you get one from a junkyard check it carefully - and it still might be most of the way along the same path of decay.

If you dont care about authenticity, get a replacement kit. JC Whitney sells them for about $ 35-40. Basically its a printed wire grid laid out on paper which is then affixed to the glass. It takes a bit of careful handling to get the thing spread cleanly and snugly attached to the rear window. Existing wiring can be attached to copper bars which are, in turn attached to the grid..