Checking for bad defrost wires.

[Jdub]

I am about to try to rectify the "bad" strips of defroster wire across my Targa rear window. I'd like to employ the method described by Brad Bergholdt, which says that each wire, as a voltage conductor, will show a reasonably bright glow at one end (positive) of the wire and a duller glow at the other end (negative) for a good wire. A bad wire shows either an unnaturally bright glow at the positive end (no ground; the tester is making this for you) or no glow (there is a break: you are getting no voltage).

Brad recommends that, for each wire, you check at about midpoint. A bad wire will not glow or glow too brightly. You move to the positive side of the wire to pick up the "scent" of current and then move to the negative side, slowly progessing until the wire no longer shows voltage.

Can anyone comment on this and tell me the BEST kit they have used to repair the bad wire?

Thanks in advance,
John

[nhromyak]

I am not familiar with this person. Is he from a Porche club, or magazine?

I have heard of a few back windows literally blowing out, because of a bad rear defrost element repair.

It is this reason, I have not tried to fix my rear window defroster. Then again, I htink I have used it twice in the last five years. My rear element only works in the VERY middle. Enough to see out of.

Good luck.

[Early_S_Man]

John,

The traces aren't wires ... they are a thick-film coating similar to the conductive compound used on metal-film resistors, and as such, I strongly suggest that you don't do any probing on known-good traces! It is possible that the pressure you apply to good traces could fracture a previously good trace!

Assuming that your two-stage defrost relay is functioning properly ... my suggestion is to determine which traces aren't heating on a foggy day or evening and mark the traces on the outside of the window ... in about four locations across the span of the window, at least once on the lateral 'down' sides and twice in the middle ... with a permanent marker. If you park the car with the back window facing the sun on a cloudless day, it may be possible to see the cracks in the traces from a back seat location.

Since a cracked trace is not conducting any current, there is no gradient in Voltage as you described! Instead, when probes are straddling the crack, you will see the full supply Voltage. I suggest probing the trace with about 6" gap between the probes ... until the break is found, then closer and closer from one side or the other, until the probes are 1/4" apart, then mark both probe locations, and another set of endpoints 1/2" further away from both probe locations. Your 'repair' section will be about 1.25" long.

The material for the repair I suggest is silver conductive 'paint' available from electronics supply stores. It is available in bottles with brush-in-cap, and also in pen/applicators, but I wouldn't recommend the pen, because gravity is working against you on the underside of the window!

The most critical part of the repair will be cleaning and preparation of the cracked trace. I suggest cleaning the area with Windex until no residue is evident on white paper towels after spraying and wiping down the damaged area ... and all wiping should be parallel to the trace! Do a fllowup cleaning with 90% isopropyl alcohol. Follow the instructions for the repair material carefully! Good luck!

[Jdub]

Warren:

Somehow I just knew you'd chime in and save me from my ignorance - thanks! I will do as you say (but first, the #$@* relay kit for my H4s).

As an FYI, Brad Bergholdt writes a car column for the San Jose Mercury News. His work is a bit "one size fits all" but then again there are a lot of cars out there to cover and relevancy probably means distance from detail.

Thanks again,
John

[Doug Zielke]

John,
When I first picked up the Blue Bomber the rear window defogger didn't work at all. Naturally, I thought the window elements were NFG. But when I checked the relay (it's in the engine room), I found it was getting no control power.
Sure enough....the infamous "suppository" fuses and their holders were corroded just enough to stop the juice from flowing.
So before you do anything else......Check the connections!

[Jdub]

Doug:

Thanks much! You know, when I decided to purchase this car (it had been sitting under a cover in front of my house for about four months - six months in the company's garage) one of the first things I did was buy three blister packs of red, blue, and yellow fuses from JohnW. Then I cross-checked the Haynes manual, owner's manual, and the fuse cover itself to make sure the correct fuse rating was in place for each fuse.

Then I cleaned every tab, checked the screws for tightness and corrosion, and replaced every fuse. Every darn one in both fuse boxes. This is the act of a man who has owned British cars (God bless 'em) and seen the evil that bad fuses cause.

John

[Early_S_Man]

John,

The funniest road test article I have ever read in my life was one in Autoweek about 20 years ago about a Lotus ... it sounded like a true adventure, or nightmare, depending on whether you were getting paid to do the test, or owned the car!

I came to the conclusion that British sports cars should have a disclaimer on the dash: "The lighting and wet-weather equipment on this vehicle are for ornamental purposes only! Nighttime and rainy weather aren't for driving this vehicle!"

[Jdub]

Warren:

I'd suffer the electrics of any Elan as long as Emma Peel was driving!

Showing my age,
John

[Doug Zielke]

Originally posted by Jdub
I'd suffer the electrics of any Elan as long as Emma Peel was driving!

Heh, heh, heh......heck, I'd even *push* the car for her if I had to!

[Early_S_Man]

John,

Yes, Dianah WAS the best TV had to offer in 1966-68 ... as I recall, even on B&W TV! And, to think I didn't find out her Elan was baby blue until the reruns appeared about 10 tears, ago!

Unfortunately, the 'haunted' test car was an Esprit Turbo ... but, 'Q' knew how to take care of them, properly!