Yep!!! They make a paint that has metal in it for fixing the problem. You will probably have to call the Glass Shop to see if they carry it. I know that Weimer told me that he used to have to repair them at Honda. If you can't find any I can check with him or can give you his e-mail addy. Never mind Poncho...I found this:
Also JC Whitney has the kit http://www.market-plan.com/jcw/14260.htm
Or here http://www.frostfighter.com/
Repairing the Grid
defroster repair paint (This is typically a small bottle of conductive epoxy paint, often colored to match the color of your defroster grid, in a kit with a small brush and piece of cardboard with a slit in it. Most auto parts suppliers (including WalMart, KMart, etc.) have these, and kits can also be obtained from JC Whitney. The usual cost is about US$10. I've repaired well-over 50 breaks using a single small bottle of paint (although I had to add some acetone to thin it when it began to dry out.)
masking tape (This is preferable to the cardboard paint guide included in the repair kits, both because you can repair a number of areas at the same time and because the slits in the cardboard are typically much wider than the grid elements.)
a razor blade (This is used to trim the edges of the repaired grid elements, where the new paint will have a tendency to wick out from the grid. It can also be used to remove the felt-tip marker or crayon elements.)
acetone (This is used to thin the paint, which will often begin to dry out in the bottle very quickly. It is only required if you have a number of repairs to make, which allows the acetone in the paint to evaporate.)
a large piece of white or light colored cardboard or cloth (This is used to enable you to see the grid elements more clearly.)
Try timing your repair to occur at a time when you can leave the FSJ for about 23 hours. I find doing these repairs in my garage on a Friday afternoon or early evening works well -- the FSJ can be left at least overnight with the tailgate open to allow the paint to dry.
While it is possible to repair the grid with the tailgate closed and window raised, this requires crouching in the cargo area. I find it better to open the tailgate and extend the window so that all of the horizontal grid elements are exposed. This also allows you to sit while working on the defroster. Be sure to support the glass (large cardboard boxes work well, and provide a place to lay the white cardboard or cloth) -- unsupported, the weight of the extended glass will break the window (in which case, ignore the rest of this and go buy another window with a functioning defroster grid!).
Make sure the defroster grid is turned off and is cool.
Following the directions on the defroster repair kit, carefully clean the broken or damaged areas of the defroster grid with alcohol to remove any dirt, oils, or other substances which may prevent the repair paint from adhering tightly.
Carefully place a strip of masking tape along both sides of the broken or damaged grid, as close to the grid element as possible and extending left and right beyond the break about 1/2" to 1". Press the tape firmly to the glass to minimize the repair paint wicking under the tape.
Repeat this until all the broken or damaged areas on the grid are masked with tape.
Carefully brush the repair paint over the breaks or damaged areas, extending about 1/2" to the left and right of the breaks or damaged areas to ensure a good contact with the rest of the grid element.
Following the directions on the repair kit, wait a few minutes until the surface of the paint has dried and repeat for the number of coats of paint desired (usually three or four). If the paint begins to dry out or thicken, add a little acetone to the paint jar and stir or shake it.
Following the directions on the repair kit, carefully remove the tape and use the razor blade to trim the sides of the repaired areas, either by carefully cutting away excess paint that has wicked out, or by carefully pushing the excess paint to the grid element. Press the side of the razor blade against the repaired area to flatten any raised areas to minimize the repair catching on the tailgate weatherstripping.
Leaving the tailgate open and window raised, wait about 24 hours to allow the epoxy paint to fully cure. (If the vehicle is outside and you don't want to leave it open, wait as long as possible before carefully lowering the window, closing the tailgate, and raising the window. You will want to minimize the possibility of the inside tailgate weatherstripping damaging the repaired areas.)
After about 24 hours try the defroster, retesting the horizontal grid elements as necessary for further breaks or damaged areas. If everything is working, use the razor blade to carefully scrape away the marker or crayon marks. (Crayon marks may smear and have to be further wiped away with a towel.)
It is not uncommon to have to repeat this process several times on a grid with a number of breaks. It is sometimes possible to hasten the process by temporarily bridging breaks with a piece of foil, allowing other breaks on the same horizontal grid element to be located. This works best with an assistant who can either hold the foil in place or hold the positive probe in place (allowing you to hold the foil); it is more difficult when working alone, although it is sometimes possible to get a good contact between the positive probe and the positive vertical element by wedging the probe into the tailgate where the positive vertical element emerges or even taping it to the glass (although it is difficult to maintain a good contact with tape).
If the color of the repaired grid is noticably lighter than the original grid (which is often a dark bronze color), the Jeep TSM suggests it can be colored with tincture of iodine.
1978 Jeep Technical Service Manual, vol. 3: Body
Haynes Automotive Repair Manual: Jeep Wagoneer & Pick-Up, 1972 thru 1991