It is simplicity itself.
There must be current flowing in the bulb filament which is a resistance to
the current. The filament will heat and you have light. Now for current to
flow you must have a difference in potential across the resistance.
So, the WHITE switched power connected to one side of the idiot light is at
12 volts and the other side going to the alternator is connected through the
some diodes to ground. Now you have a difference in potential when the key
is switched on. As the diodes start to develop a voltage level and it gets
to 12 volts the light goes out. If the alternator voltage output begins to
drop down and the voltage level goes low enough the light will come back on.
This is the basic theory. In reality it requires more explanation on how
all this plays but this is the basis for the idiot light function.
I am sure someone will comment on how the voltage on the starting diodes
initiates the alternator charging circuit and why the light does not come on
when the output from the alternator goes above 12 volts. But for a basic
understanding I think this covers the subject.
Ross "Commodore Blues" Hulse
Sent: Saturday, September 06, 2008 5:30 PM
To: Beamclub
Subject: [Tigers] Fw: Re: Ign/ Gen idiot light
--- On Sat, 9/6/08, Tony Somebody <achd73@yahoo.com> wrote:
> From: Tony Somebody <achd73@yahoo.com>
> Subject: Re: Ign/ Gen idiot light
> To: "Mark VT Tiger guy" <coolvt@aol.com>
> Cc: tigers@autox.team.net
> Date: Saturday, September 6, 2008, 7:10 PM
> First I want to Thank Theo, Curt,Dan and others Ive missed
> who sent information concerning how to fix my problem w/ a
> one wire and the idiot light. SNIP---
I know
> that years ago someone explained the theory of what makes an
> idiot light work but like many things, the older I get the
> more I forget. Will those that know or even think they know,
> explain just exactly how the idiot light works. Thanks,
> TonytheTiger
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