My engine has had a replacement alternator installed by the previous owner and the tachometer doesn't work at present. This alternator has only three connections - B, L (light, I think), and R (field, I think). My understanding is that to connect up the tachometer from the switch panel it needs a fourth connection (usually w) and this is shown in the engine wiring diagram (below).
Is this true? Or do I just use one connection - R?
I am a bit confused because the diagram seems to show the tach connected to both R and W:
Any advice welcome.