300 d turbo alternator wiring

[pjl]

Hi, quick question...I have a 3 pin alternator marked D+] ] ] B+.
The middle and the B+ go to the positive batt. terminal. The D+ goes to a dash light. I'm putting this in my Unimog, with a voltmeter. What do I need to do with the D+ circuit to make this work? I have a wiring diagram, but am familiar with domestic and asian wiring. I can't decifer which way power flows through that circuit. Appears to have a keyed positive feed through light to alternator.
Thanks in advance, PJL