Hello
Here's a short guide on how to replace the speedo cable.
1) Jack the car up. Ensure it's safe by giving a little push and pull action. I would HIGHLY recommend axle stands.
2) Locate the speedo cable underneath the tyre.
3) Take the hub cap off. i have radial wheels, so your may be different but on most Beetles, the speedo cable will enter the actual wheel in the same place.
4) Un-coil the small wire which keeps the speedo in place.
5) KEEP IT. This piece of wire is replacable, but it's just easier if you keep it safe.
6) Unscrew the speedo cable from the back of the speedometer.
7) Push the speedo through the wheel and pull it up through to the bonnet.
You should then be in a position to put the new one in making sure you clip it in the right places (under the car). There shouldn't be much extra wire, so routing it to keep everything neat isn't really possible.
8 ) Screw the new speedo in!
Make this the last task. The speedo cable should be connected to the wheel, the hub cap back in place. You can test it now by turning the wheel if you wish. The small metal section in the middle of the speedo cable should also be turning. If it's not, there is something wrong.
It will probably take a few miles to bed in properly. Make sure you give it a good go by not only driving 50mph, but also at 5, 10 and perhaps 15, giving the speedo a good range to get used to.
If you want to recommend any changes, let me know.
Thanks