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Re: turn signal



Regarding Matt C.'s comment:

Everyone is correct. Most auto manufacturers use this old (but well
tested) method of telling the drivers there is a bulb out. The
flasher, that's really what it's called, is replaceable like a
relay. When voltage is passed through it and out to the bulbs, the

"Voltage passed through"? Perhaps you mean charge and/or current
passed through?

plate or strip inside it heats and causes the regular breaking of
the circuit as bc said...but, it's actually the LOWER resistance in
the circuit, because of an absent bulb,

Actually the front bulb and the rear bulb on a given side are in
parallel. Opening the filament of one of them *raises* the
circuit resistance.

which causes more current to pass, faster heating of the strip and
the quicker flash rate. Hope this helps!

The details of the overall flash rate are tricky. Typically an
increase in 'on' current shortens the 'on' heating time but
lengthens the 'off' cooling time. The overall frequency can go
either way with an increase or a decrease in circuit current.
depending on the thermal/mechanical response characteristics of the
flasher element. I suspect that in Carl's car (only 8 years old) the
flasher might even be a solid state electronic device rather than a
bimetal heat/cool make-break contact interruptor.

Matt Coia
Undergraduate Assistant, Physics Education
Buffalo State College
oh...and ASE Certified in Automotive Electronics :)

David Bowman