Ok, you should usually have 3 wires to the alternator, the battery feed, the one from the ignition light which you can find with a meter, the rev counter and perhaps a supressor (little black box perhaps?).
Can't tell you the colours off the top of my head but the thick one is obviously the battery, then look for a wire that's live with the ign on but the engine not running and connect this to the field or exitation.
If you know electonics at all the alternator comes from a single phase tapping out of the 3 phases on the alternator, so will show some sort of continuety with the battery terminal.
Perhaps the eaiest way though is to have a look inside, the ignition lamp wants connecting to the voltage regulator.