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Old 12-06-2003, 03:38 AM
pjl pjl is offline
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Join Date: Nov 2003
Location: Kelowna, BC
Posts: 21
300 d turbo alternator wiring

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
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Old 12-06-2003, 09:43 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
You got it. The circuit is from battery power through the light and into the alternator, where it grounds through the rotating winding. It is the activation circuit and as the small field is rotated a set of diodes, normally called the trio diode or the excitation diodes, breaks out a larger current flow to the rotating field (through the regulator). At this time battery voltage is on both sides of the bulb filament and the light goes out.

Often in the field we have used a test light hooked to battery + to activate the alternator. Any small wattage 12v bulb wired in series from the battery will do the job. It would be prefered to have that circuit powered up by the ignition key.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 12-06-2003, 12:38 PM
pjl pjl is offline
Registered User
Join Date: Nov 2003
Location: Kelowna, BC
Posts: 21
One more for yah

Excellent, thanks for the quick informative reply. Just to expand my limited knowledge of alternators, where does the light ground if there is a charging failure? Does it go all the way through the alternator. I see another unfamiliar symbol (wiring diagram) of something attached to the light which may be a ground or resistor or ? It's not labelled, maybe ammeter/voltmeter.
Thanks PJL
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