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alternator wiring

uid 18083's pic
posted by  lucid on  Mon Nov 8 05:02 CST 2004
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last visit: Fri Oct 24 12:31 CST 2014
[RELATED]

So my question is, where exactly does that red wire terminate?
Ans: It goes to (actually comes from) the BATT light bulb.

The current drawn by this bulb (and 3 others) when the Key is first turned ON is called "pre-exitation current", and is essential to getting any alternator output.

In normal operation, that should be the ONLY time current actually "flows" thru that wire. Once the Alternator is putting out 13-14 volts, that D+ "field terminal" rises to the same level as the B+ output.

That's what puts the light out—Key on voltage on one side of the bulb VS Alternator voltage (from D+) on the other side. Plus-to-Plus means no current flow, so the bulb goes out.

I'm not sure that running +12V straight to D+ (i.e., "hot wiring") is a good idea, as compared to duplicating the normal circuit from the firewall plug forward. There is usually nothing wrong on the Bulb side, unless the bulb itself is bad.


--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.






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