It's on the gearbox near the differential and driveshafts.
what does it look like?
The speedo works sometimes but then drops when driving. i have spoken to an auto electrian and he has advised that this could be the problem.
It could be the problem or it could just be the connections are dirty at the plug.
The wiring should have 3 wires going to the plug and be gray, yellow and black.
Plug should be about 1" square.