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  1. #1

    Default Resistor? Ammeter? What is?

    Can anyone identify this electrical component? It is located under the starter relay bundled into a wire harness which runs along the engine well and under the battery box. 3 wires attach to a quick disconnect into the ignition control module box ( I think). Can I replace this, if so with what?Name:  IMG_0008.jpg
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  2. #2
    FEP Member Mgino757's Avatar
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    I'm also curious as to what this is. I noticed it when I redid my voltage regulator wiring.
    1985 Mustang GT conv. modified 4180C, Weiand Street Warrior intake manifold, equal length headers, true dual exhaust, 3.55:1 8.8'' rear end, 180* thermostat, Ford Racing 10.5" clutch. Garage dweller.

    1998 Mustang GT auto. Stock and slow daily driver.

    1996 Thunderbird LX 4.6L V8. Wrecked, drag racing in heaven. RIP Oct 1995-March 24, 2016.

  3. #3
    Thomas

    1985 Mustang GT - Build Thread
    347 (10.5CR, AFR 185's, PP Crosswind, Comp Custom Cam, Holley SA "670"), T-5, 8.8 w/3.55's, MM SFC's, T/A, PHB, LCA's, STB, KMB, Bilsteins, MM/H&R Springs, SN95 5-Lug, Cobra Brakes

  4. #4
    FEP Member Mgino757's Avatar
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    I'm trying to figure out why my ammeter doesn't work. I guess I'll have to pull the cluster to make sure it's still good.
    1985 Mustang GT conv. modified 4180C, Weiand Street Warrior intake manifold, equal length headers, true dual exhaust, 3.55:1 8.8'' rear end, 180* thermostat, Ford Racing 10.5" clutch. Garage dweller.

    1998 Mustang GT auto. Stock and slow daily driver.

    1996 Thunderbird LX 4.6L V8. Wrecked, drag racing in heaven. RIP Oct 1995-March 24, 2016.

  5. #5

    Default

    The ammeter runs off a very small voltage generated by a short length of resistance wire in the harness. 'Very
    small voltage' means the ammeter will hit the peg with about 50mV across it, so be careful when you're trying
    to test the gauge.

    The resistance wire forms what is known as a shunt, because, well, it's shunting off a small portion of current to
    the ammeter. It lives between the main feed at the starter relay, and the junction where that main feed joins the
    charge lead from the alternator. Current flowing through the shunt wire creates a small differential voltage. The
    polarity of that voltage depends on whether the current is flowing into, or out of, the battery. (BTW, this shunt
    arrangement is why Ford ammeters don't cause fires like other ammeters were known to do back in the '50s and
    '60s.)

    Since it's dealing with such small voltages, ammeter problems are usually caused by oxidation in the connections
    under the dash, and/or on the back of the instrument cluster itself. (Or if the shunt was bypassed as part of a 3G
    alternator swap.)
    Last edited by JACook; 02-21-2018 at 05:04 PM.
    Cheers,
    Jeff Cook

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