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Adding a Rear Window Defroster

Contributed By: Bill Kelsey

Adding a defroster is no big deal -- the circuitry is very basic. In the Jeep, it is just a circuit with a 10 minute automatic shutoff timer built into the on/off switch & light. Your fuse block should already have a place for it.

The biggest problem in actually adding a defroster is getting the defroster grid to fully adhere to the glass. The glass has to be very carefully prepped (usually cleaning it with something like Brasso to strip away anything (dirt, grease, etc) before applying the grid strips, which typically come on 3-4" paper rolls with several strips to a roll, with adhesive already on the strips. Kits with all necessary parts should run about $40.

In my experience, the adhesive has a tendency to soften and lose its grip if the defoster gets very wet (as in frost on the inside of the window) and hot (as in using the defroster), although supposedly the adhesives have improved since I last installed one of these kits.

FSJs present another significant problem. Because the tailgate window can be lowered and raised, anything mounted on the glass runs the risk of being snagged and pulled away. If the add-on grid strips are not absolutely flat to the glass, you will probably run into problems. This effect is strong enough to wear the grid strips on the factory glass, eventually rubbing off the sections of the conductive paint (so that there is no actual break in the underlying metal grid -- but the current is so reduced that the element won't function).

Anyway, you might find the best option is to get a used FSJ tailgate window with factory defroster grid and install that. If the grid is damaged (broken or the paint is worn away in parts), the repair is simple, although a bit tedious. The biggest problem is locating the breaks (you need to measure the voltage along the grid strips), and this is no big deal. The readings will also alert you to areas on the grid which still work, but where the conductive paint is getting thin and will probably fail soon.

The conductive paint used to repair the grid can be bought at most auto parts stores for about $10. The bottle of paint is very small, but in my experience it should be sufficient to repair about 50 normal grid breaks.

There are some tricks to making the job easier on an FSJ -- work with the tailgate open (and the glass well supported!); have a strong contrast material (white works well) underneath to help you see the grid better; use magic marker instead of crayon to mark the breaks (much easier to remove); ignore the paint guide that comes with the paint (usually much wider than the grid strips) and just use masking tape (carefully applied); keep the paint thin with acetone (it takes a little longer to dry, but is smoother); and use a razor blade to "push" the edges of the new paint in, or to trim the edges away, to keep the grid straight and neat looking (the paint tends to feather out, even when not thinned with acetone, especially if the glass is scratched).

Bill Kelsey
Aberdeen, SD
'79 widetrack Cherokee "S"

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