Thanks for the replies so far. My truck only had the Battery connection and sensing wire connected when I got it, and charged the battery OK without the field connection being connected to anything.
I was going to connect the warning lamp/LED to the the Field terminal that wasn't connected before. I'm just not sure whether an LED will work OK with the control unit in a 10SI alternator because of the tiny amount of current that would be flowing in the field circuit, so wondered if anyone had tried using an LED before with this particular alternator/control unit setup.
Understand the the 10SI connections look like this.
http://i103.piczo.com/view/3/h/b/5/2/u/p/w/0/w/z/t/img/i287317235_31052_5.jpgStuart.
