With the OE style cable, which is what Jessie describes and most likely what you have, loosen the adjusting mechanism. The parts, being plastic, shouldn't require any solvent. There is a barrel, for lack of a better term, which is the big piece with flats at at the rear and bushing which protrudes from the front. The threaded part of bushing is split and clamps down on the cable as you screw it into the barrel. As you back it out it frees up.

Use an open end or adjustable wrench on the flats at the rear of the apparatus and slip jaw or channel lock pliers to free up the bushing at the front.

You just need to loosen it a bit to the point where you can turn the the two parts as one with not much effort. Use the open end on the flats for this part of the procedure. If the bushing is so loose that it won't turn with the barrel run it in a bit. Still, you may have to turn one and then the other incrementally.

Make the adjustment. When it's within spec, immobilize the bushing with the pliers and tighten by turning the barrel only. Don't over do it.

If it's a Sach's style cable, they are pretty much self-explanatory.
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'80 DL 2 door, '89 DL Wagon