Look at the middle of the diagram. The large white rectangle represents the engine ECU and marked as 1320. You are looking for the 48 Pin BROWN connector, which is show on the top left of the ECU (48V MR).
Wire 6738A is the engine speed signal, shown in pin G3
Follow this back to the vehicle speed sensor shown as 1620 in Pin 3
So I would check the wire conditions at each end for condition.