Quote:
Originally Posted by gamefreakgc
Would that have to do with the LED's not providing any resistance in the wiring? I replace a few bulbs in the dash other than the backlights with no issue but I didn't touch the CEL as I wanted it to be orange and noticable.
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The 'old-school' way that Toyota did the low-fuel light is an NTC thermistor in series with a bulb. When the thermistor is submerged, it is cooled and stays high resistance - not enough current flows to light the bulb. When the thermistor is out of the fuel (low level), it drops in resistance, current goes up (and heats up the thermistor more!) until there is enough current flow to light the bulb - this increases resistance in the circuit and limits the max temp for the thermistor.... you don't want something hot enough in there to catch it on fire! That feedback/interaction between the bulb and thermistor is what gives you that slow on/off effect.
If you use an LED in place of the filament, the small current through the thermistor is still enough to turn it on - and the high resistance of the LED (compared to a cold incandescent filament) keeps the thermistor from ever changing state - you should just get a dim-ish light all the time.
The '99+ just use a comparator in the gauge cluster for when the level gets low enough (also a different sender style, etc.).
-Charlie
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