Strange alternator voltage

[red griff 500]

My griff 500 has a magnetti marelli alternator with 4 cables, three in a group which I believe carry the current to the battery (2 cables)and a voltage sense wire. However, the 4th cable (a thinnish black one) is connected to a screw post which is insulated from the alternator body, and the voltage on this post is about 1.3v relative to earth. The reason I found this out was because my otter switch uses it as a ground, and the fan relays weren't switching reliably. I've since changed the otter switch ground and solved the problem.

My question is, what is this terminal used for, and should it be at 1.3v?

Steve

[pedroman]

not sure. I have a spare as i had erratic voltage readings on mine and changed it under warranty. New alternator costs over £500. Yikes. I seem to remember the discovery had a very similar magnelli one and the haynes manual had an exploded diagram, not sure if it gave any voltage outputs or explanations though. Can u compare with another?

[david beer]

I think it was used for the rev counter on a Range Rover, does it go up with revs ?

[red griff 500]

Not sure whether it changes with revs - I'll cvheck it. Another possible explanation is that it is something to do with the voltmeter, or the charging lamp in the dash.

Steve

[david beer]

I think you will find the other used one is the ignition light. There is also mention of a "split charge" system, where two batteries are used.