Alternator W connection

[Ancient Mariner]

I used the wiring colours suggested by garrycol for the tacho and tried it on our crane which has a W terminal on its alternator .Works but out about 750 rpm.I then pulled the Isuzu alternator to pieces to solder in wire for the W point reassembled but no work:( Have I picked the wrong wire?:confused:Any help appreciated

AM

[steveG]

I'm not an autoelec, but pretty sure you've got the common point for the windings there.
You need to tap into one of the windings just before a diode. I'll see if I've got a photo around from when I did mine.

I also recommend adding a resistor to the wire close to the alternator to limit current if your tacho wire goes short circuit anywhere. I just about torched my County with a tacho wire that shorted in the dash. Think I used an 820ohm from memory. Think I calculated it on a 100ma current draw which is plenty to trigger the tacho, but unlikely to melt the wire.

Steve

[Bearman]

I have a Hitachi 12V 70A from a 4BD1T with a tacho wire sitting on the bench in the shed. ****ing down with rain here atm but I will pull it apart later and post up a photo of the wire connection.

[Ancient Mariner]

The reason I used that one is I took it to a autolec who said he was`nt sure and that he was not familiar with the four wires and they usually have only three .Of the four wires three are double and one is single I have tried all wires without result. As the tacho is only adjustable via a computer program I have ordered a new one and will see how I go with that
Thanks Noel

[Bearman]

Here we go Noel. You can see the wire is attached to the left field connection wire. I know this works as I had it in my vehicle with a VDO tacho.

[Ancient Mariner]

When I pulled the Alternator to pieces I expected to 3 wires with either one to be used as the W connection .When I found 4 lots I was a bit :confused: but soldered a wire on anyway.When it did`nt work that is when I consulted the autolec who said unsolder the diode plate and solder it where it is in my pic:mad: That didn`t work either so ordered a new Tacho Just hooked it up as
Brians picture showed and spun it up in the lathe:):D:p Many thanks fellas hope you did`nt pull it apart just for the pics Brian

Thanks Noel

[Bearman]

No problem Noel, only a 10 minute job. Pleased you got it working.:)