Aside from replacement ($100 part), this is the next best thing to do, and it's not all that difficult. I actually kind of enjoyed doing it.
Trunk Wire-Harness Repair
2004 Saab 9-5 Sedan
One of the Saab 9-5 sedan's few design-flaws is that the wire bundle that runs from the car body to the trunk lid makes a 180 degree turn around the sharp edge of the plastic elbow in the lid. This eventually leads to broken wires and some fun electrical situations. These wires power the reverse lights, fog lights, latch actuator, anti-theft micro-switch, and license plate lights. You might notice for example if the micro-switch wire breaks the trunk can be wide open and the dash won't tell you, or you can open the trunk without the alarm going off, and the light in the trunk won't illuminate. My actuator wire broke so I had to crawl in through the back seat to pull the emergency release cord.
First off, you need to remove the lining on the trunk lid. There are a bunch of those push-pin fasteners along the edges, and you need to unscrew the torx screws that hold the grab-handle in place. If you have an earlier 9-5 with the warning triangle mounted in the lid, I couldn't figure out how to remove the brackets without breaking them when I did this repair in my 2001. In my newer car, a 2004, the triangle was deleted, but I still had to destroy the two black fasteners to get them out. If anyone knows secret I don't I'd love to hear it! If your 9-5 has the emergency pull release, the cable slips out of the clip so you can pull the handle off.
Circled below in red are all the harness connectors. From left: reverse/fog housing, micro-switch to tell anti-theft the trunk is open (top), license plate lights (bottom), trunk actuator, and the other reverse/fog light housing. Circled in green is one of the white clips that hold the wires against the lid. Bend them to one side and wiggle a little and they come out pretty easily. I labeled all the connectors before unplugging them but probably could have managed without that step.
In the trunk now, open the door to access the brake lights on the driver side. The green bundle of wire in electrical tape going to that white connector is the trunk lid harness. Release the tab on the connector and unplug it.
If you stand to the side of the car and twist the plastic elbow that runs into the trunk lid clockwise and HARD, the right-side clip will release (sounds like it's breaking, but it shouldn't) and the left side then slides out. Where the harness runs into the body of the car is just a rubber hose and it pulls right out. The hard plastic tube clipped onto the hinge assembly next to the gas lift un-clips from the hinge.
Here's what it looks like out of the car:
I bought some 18 gauge automotive wire from Walmart and shrink tubing from Radio Shack. I spliced in about 12" of wire, but you might even want to do more so that your splice connections on either side can be in the car and in the lid and not running between. I crammed all mine into the hard plastic tube attached to the hinge so they wouldn't bend. For the splices I cut 1/2" of insulation off the ends, twisted the wires together, soldered them, and used a heat-gun (HOT - BE CAREFUL!) to shrink the shrink tube.
Now you just feed the harness back into place. I wrapped the section of wire that bends tightly in a couple layers of electrical tape to give the bundle some rigidity. Hopefully it will last!