Bspikes

ok, so here goes. The speedo in my car does not work, well it works randomly but incorectly. Most of the time it is pegged all the way over. But ocasionally it will start to read backwards. This usually happens when Im on the freeway. It will move backwards, counting down speed instead of increasing speed. The faster I drive the farther it goes around. I have checked the harness behind the dash for cuts or damaged wires and have found none. I have checked the connection at the VSS, looks good. The other gauges work, temp and fuel. The tach doesnt work but thats because the DA before me cut the harness to install an after market coil. Any help with this would be greatly appreciated.