Is it as simple as cutting one wire
Yes, but there is a better method
Where do I cut
At the RSW terminal on the ECM (Electronic Control Module) near the glove box
Which wire
Violet with red tracer
What are the implications
The engine warning lamp will light
Will my speedo still work
Yes, if you have cut as above. No, if you cut the wire between the vehicle speed sensor and where it branches off to the speedo.
Can I fit a switch to turn it on or off
Yes, then you can get rid of the engine warning when its on
What is the better method
Fit a "Speed limiter defencer" - a small box which will reduce the number of pulses passed down the wire, thus raising the speed limit. If inserted in the line as described above, it will not affect the speedo reading.
Why doesn't everyone do that, then
Typically, the device costs about £100 , and it needs to be supplied with 12V power - the latter point should not be a deterrent
Could I make my own
Yes, the components should be relatively cheap. When you've got it working, let me know what you used, so I can make mine