Alternator electrical expert needed

[red griff 500]

I've got a Magnetti Morelli alternator on my 94 Griff 500. The charging light comes on when I start it up and doesn't go out until I rev the engine above 2000rpm. Once it's out, it stays out, even when the revs go down to 500rpm (nearly stalled). There's an electrical screwed post on the back of it, and the wire connected to it disappears into the loom. I know that this was originally connected to the earth side of the Otter switch and I disconnected it because the cooling fans relay didn't work properly due to the fact that this post was not a good earth. I connected a good quality earth onto the Otter switch and have never had a problem with that since. The voltage on this electrical post varies up to 7 volts, I dont know what else it's connected to, but I know that when I re-connect this to the Otter switch the light goes out at about 1200rpm.
I wonder if this post requires a voltage to start the excitation of the electrical field when the alternator first starts rotating? If so, what voltage should this be supplied with? an anyone tell me the voltage on this post on their MM alternator?
I've fitted a new alternator in the past and it works in exactly the samr way as the original.

[blitzracing]

Its not so much a voltage, but a certain current needed to "excite" the alternator field windings to get it to start to generate a voltage. Once its started, the alternator supplys its own current, so the lamp goes out. If the initial supply current is lower, you have to rev it harder to get the charging to start and vica versa, but its not a problem either way as long as the light goes out.

[jimed]

It may not be relevant here but for the S series (V6 at least not sure about the V8) you have to rev it to 2k to get the charging light out then after the initial rev it is OK as you say down to tickover and it stays out. That is apparently a quirk of the way the S series electrics are set up - could be the same on your Griff but then wouldn't they all be the same?
Jim

[red griff 500]

Thanks for the replies chaps - I agree that it's not a technical problem, but I find it annoying and I'd like to make it better. There must be a way of improving it, after all, I dont suppose all Griffs and Chims behave the same way. I know that this post is capable of delivering a high current because when I connected it to earth (which is what the relay required- the original problem i was trying to fix) the wire got mighty hot.
Anyone know what this post should be connected to?