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Voltage ONLY when engine running, NOT ON position...

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  • Voltage ONLY when engine running, NOT ON position...

    I've seen alot of posts regarding people who want VCC trigger only when the engine is actually running, not just in the ON/IGN position with engine off, so after finding dead ends in both cabin and engine bay fuse boxes, i snooped around and found a plug on the alternator which has 4 wire square harness (civic 8th gen). One of thgose wires actually tested 12v VCC only when the engine was actually running, it is the blue white stripped wire, so if anyone wants to find theirs, test your alternator outputs you might succeed
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  • #2
    also, never use these as direct power sources, always run them to a RELAY and use another power source (battery) for your accessory(s).
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    • #3
      White / Green is alternator control signal (ALTC) goes to ECU
      White / Red is alternator FR signal (ALTF) goes to ECU
      Black / Yellow is power to ignition goes to under dash fuse/relay box
      White / Blue is charging indicator light in dash
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      • #4
        Yes - you have essentially described what many use for "engine running" signals.
        For EFI systems, air flaps and injector pulses etc can be used whilst for all petrol vehicles, spark sensing can be used - noting that all of these are "active" during cranking.

        But the alternator's charge-light circuit is the choice for those wanting the "not cranking but is running" signal (for most alternators - some may extinguish the D+ or L light during cranking).

        D+/L is often used used for fuel pump relays & fuel cut & electric chokes with an added "prime" (cranking) feature.
        D+/L on its own is often used for battery isolators and certain loads (DRLs, heavy lights etc).


        Whilst DP or other ECU controlled alternator signaling can be used (with filtering etc), the simplest is the traditional charge light circuit which is traditionally low (grounded) when not charging and +12V else floating when charging.
        For those lacking that function, VSRs (voltage sensing relays) can be used (as used for other battery isolators but without the associated delays).
        Last edited by OldSpark; 10-20-2013, 04:38 PM. Reason: DRLs

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        • #5
          Thank you for the information but I just wanted to mention you have probed all 4 of those wires and exposed them to the elements. 1 winter or less and the copper in all 4 of the will be green and corroded and there will then shortly after be 1/4" of copper missing inside the wire casing. It may happen a little slower depending where those wires are located but still a potential problem. You may want to try to seal them back up...
          My 2007 Ford F350 Work Log located HERE

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          • #6
            Already sealed
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