The Civic VTi sends an electronic signal via the VSS located at the back of the gearbox.
http://hondacivicrepairs.com/views/h...or-profile.JPG
It is easy to remove and visually check. Just undo the small bolt that holds it in, jiggle it and pull straight up. Check the nylon wheel for wear.
The other thing is check the plug for damage or the wiring.
You could swap the unit out with another to check its operation.
I don't think the problem will be in the cluster, but if you can get hold of another cluster (with tacho) you can check.
Peter