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Indicator LED's for automotive use

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John D

New Member
Newbie here, looks like a great site!

I've got an old El Camino , and I'm converting it to the factory guage option. I'm in the process of restoring the guage cluster itself, and an idea hit me.

Why not install a small, high intensity LED into the guage face, and have it turn on when the "danger zone" is approaching? Very similar to how a modern cars "low fuel" lamp comes on. Just an attention getter.

Here's the rub (s)....
1) 12vdc, neg ground system
2) The impedance of the circuits/sending units is in the range of .5Ω to 90Ω (cold to hot - temp guage, full to empty - fuel guage)

Any circuit or driver ideas?


Well-Known Member
Most Helpful Member
Once you have the gauges working, look at the voltages at the gauge inputs. Most automotive gauges are fairly constant resistance, and the senders' resistances vary. The voltage at the gauge inputs will be a reasonable measure of fuel level, engine temperature or whatever.

If you have a voltage comparator with one side the gauge input and the other side a trimmer potentiometer, that should light your LED when needed.
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