You can follow Volvo From Heck above and Nahtanha advices on that repair. It is quite simple to do.

I have done many grid repairs on the 1982. It is the age factor and use of an ice scraper that do affect the printed circuit. I have used Permatex quick grid rear window defogger repair kit with success. The small bottle contains silver, ethyl acetate, ethanol and 2-ethyoxyethyl acetate. Flammable mixture it is.

Once opened the bottle will not close tight and it is thin glass, the residue will dry over a year or so. But I found a way to re-use it. Having worked in a chemical lab over 34 years I tried a few things. I add a few drops of acetone, a few drops of lacquer thinner and I use a small polythene rod to finely crush the solid lumps dried at the bottom of the bottle. I have sometime used a small flat screwdriver to carefully breack loose the solid lump.

I found that having a voltmeter connected to ground and probe inside from left to right with the grid heater ON Will bring you to the exact line break.

Inside the car and starting on the left at 2 inch from the edge you should read 0.2 to 0.5 volts. If you read 12 volts the cut is on the left. If you read 0 keep probing toward the right and you will find a break that you can mark just over with a felt pen.

It is easier to see the break point if you look outside near your pen mark and make a more precise mark.

I apply 2 coats of that silver compound.

You may have more than one break on each line if an ice scraper was used.