92-93 Inertia Fuel Shutoff Switch Reset Indicator

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Most earlier trucks used a 2-pin (SPST) IFS, which won't work this way. Later trucks had the SRS light where the fuel reset light was, so that's why this is described for only '92-93 trucks.

Although '92-93 trucks contain some of this wiring, none were built with this circuit, or a bulb in the instrument cluster for this function. And some have the wires in the wrong places on the IFS connector (C271). But with a little effort, this circuit can be added to those trucks.

With a little more effort, it can be added to most others with an SPDT inertia switch, or this switch could be swapped in.

When the IFS is set (normal), the ground for the bulb is open-circuit (off), even when the key is in START or RUN and supplying 12V to the bulb. When the IFS is tripped, the circuit is completed through the fuel pump motor to ground. Since the motor requires far more current to run than can pass through the tiny bulb's high resistance, the bulb lights, but the pump doesn't run.

I suspect Ford deleted this circuit because it supplies power to the pump (albeit a tiny amount) even when the IFS is tripped, which risks starting a fire.

See also:
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Owner caption September 2016 · Photo 0 of 5000