Here are the pictures and instructions. This TSB is easy to do, and the range in my key remote went from 4 ft to 30 ft.
1999 996 Cabrio. Here are the tools you will need.
The following steps:
1. Remove the sun visor. It simply pulls out
2. Use the small flat screw driver to pry of plastic cover on visor base. When removed, you will see the Hex bolt heads
3. Use the 4 mm Hex wrench key to remove both bolts. Hold on to the part, it has washers on the other side and can get fall off if not careful.
4. Now pull off the A-pillar cover to reveal the cables underneath.
5 Pull out the cables that are held in place on the foam sleeve. There is double sided tape holding it in place, pull carefully but firmly. From the top down
6. After pulling it, undo the foam by pulling apart the seam. The white wire is the antenna we are looking for.
7. Keep peeling off the foam until you get to the black sleeve on the antenna.
8. Measure off 130 mm from the end of the black sleeve upwards into the white antenna, and cut the the rest off. You need to keep 130 mm (25 mm is about an inch) of antenna above the black sleeve.
9. Pull the antenna wire off the foam sleeve, and enclose the rest of the wires with the foam sleeve.
10. The picture shows the wire after being secured with electrical tape to the OUTSIDE of the sleeve, and towards the inside of the cabin when the foam is taped back to the A-pillar.
11. The two sided tape on the foam is sticky enough to simply push the foam back into its original position.
12. TEST the remote now before assembling the trim. Walk away from the car, lock and unlock it, and grin.
13. Replace the trim, it just pushes back in, do it from the bottom up and ensure it is on the inside of the rubber gasket.
14. Secure the sun visor base with the two Hex bolts. Careful you don't loose the washers. Then push back in the sun visor and you are done.
I changed from the TSB the location of the antenna wire to the outside of the foam sleeve, and added the bit of electrical tape to hold it in place and avoid any issues when reassembling the trim.
It worked for me and I have tested and enjoyed up to 30 ft of range with the remote in open lots, and covered garages.