Alternator connection for tach
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.
Your link doesn't appear to work. I would think that the "R" terminal is connected to the internal regulator, and extenally to the "ignition switch. (It is for Hitachi alternators anyway).
IMHO, you need a dedicated tacho "W" terminal to give the necessary AC output. The other terminals connect to the battery one way or another and will not give the frequency signal.
Link seems to be working for me - it is: http://www.pinksgreen.com/wiring.pdf
Alternator is a Mitsibushi 50A 3 wire alternator. Should have said that.
Thats better, dunno why the first link does not work.
Originally Posted by dgadee
The signal to the tacho comes from the W terminal via wire 10 in the diagram
It is a direct connection to one of the stator coils. Ie it is unrectified AC.
Sometimes it is a tapping off the coil to deliver only 8 volts I beleive.
Other connections to the tacho are the positive and negative power supply and to the illumination bulb.
For some reason, the 2nd link works for me. Don't understand why wires 10,11 and 12 all seem to be joined at the connector, perhaps I'm misinterpreting.
I would expect the tach to have a 12v power connection, + & -, and a separate signal, (W) connection.
Perhaps someone else can expain.
I think I get it now. Will take it over to my car electrics man and see whether he will add a w connection to it for me.
Yes you are misinterpreting the representation of the 12 way connector
Originally Posted by earlybird
Tach connections explained while you were posting
The one bottom right goes via wire 5 to earth . the one bottom left is the positive ...
Last edited by VicS; 05-04-11 at 20:31.
I'll defend myself; that's what it should be in reality, and that's what I said I'd expect, but it's not what the diagram shows. eg; upper right teminal on "B" appears to indicate wires 10, 11 &12 all connected to the same terminal. Lower left on "A" shows 10 & 12 apparently connected. That was part of the OP's problem I think.
Originally Posted by VicS
Must have been drawn by the apprentice draughtsman.
Last edited by earlybird; 05-04-11 at 20:46.
It is for a vetus m3.10, so presumably a Dutch apprentice.
Or maybe double dutch.
Originally Posted by dgadee