Turn signal comments (long, dull read)

["Terry & Andree Hoeman" <tehoema@xxxxxxxxxxxxxx>]

You did it again Dick.

I never knew that was the difference between types of flashers.

As always -----thanks for the enlightenment.
----- Original Message -----
From: "Dick Benjamin" <dickb@xxxxxxxxx>
To: <mailing-list@xxxxxxxxxxxxxxxx>
Sent: Monday, April 07, 2003 11:49 AM
Subject: IML: Turn signal comments (long, dull read)


> A question about why turn signals sometimes won't flash but just stay on
> steady (usually when a bulb is burned out) has come up before here, and
> yesterday one of the IML members asked me privately again about this.  If
> anyone is interested, here is my reply on the subject:
>
> First:  the question - - -
> > To: "Dick Benjamin" <DickB@xxxxxxxxx>
> > Sent: Sunday, April 06, 2003 10:08 AM
> > Subject: turn signal
> > Dear Dick,
> >
> > I'm sure you've forgotten this, but several months ago we had a
> > discussion on the IML regarding a non-functioning turn signal on a '68.
> > I told the person posting the question to check & make sure that all his
> > taillight bulbs were working, because my turn signals will not function
> > (blink) if one bulb is out.
>
>  Well, last night I noticed
> > that one of my bulbs was out (the furthest left one) and I just replaced
> > it.  My turn signal now blinks again.  (It used to just come on and stay
> > on, but wouldn't blink.)  I knew I wasn't crazy!
> >
> > Do you have any idea why this is?  You mentioned something about needing
> > some sort of "interrupter"--? Not sure about that.
>
> and my comment:
>
> There are two types of flashers utilized in turn signals.  One type is
> independent of current drain (meaning number of bulbs on the circuit) and
> one is dependent on the number of bulbs to set the flashing rate.   The
> former type will flash no matter what load is attached to it; this is
> required if the number of bulbs on the circuit will change from time to
> time, as would occur if one occasionally towed a trailer.  If you go to
the
> auto parts store and look through the store display, you'll see both types
> mentioned.
>
> The one with which most cars come equipped from the factory is the type
> which is sensitive to the load, because it gives a sort of poor man's
> warning of a burned out bulb by ceasing to blink.   I haven't checked on a
> 68, but I'd guess this is noted in your owner's manual as a symptom of a
> burned out turn signal bulb.   If a car had ever been used to tow a
trailer,
> the flasher would probably have been upgraded to the more expensive but no
> longer load sensitive type, or else the flashers would have blinked super
> rapidly when the trailer was connected.
>
> I don't know what would have elicited a mention of "interrupter" by me -
> unless perhaps I described the flasher operation in excruciating detail
(see
> below).
>
> The way the flasher sets it's flash rate is by allowing current to flow
> through a coil of wire which is wrapped around a bi-metallic switch arm -
as
> the current heats the arm, it bends and breaks the circuit momentarily,
thus
> "interrupting" the current momentarily.  As the arm cools, contact is
> re-established, repeating the cycle.  The repetition rate is thus
controlled
> by the amount of current flowing.  If the current flowing is insufficient
to
> heat the arm to the contact breaking point, the turn signal bulb will just
> light and not flash at all.   This is what happened with your car - the
loss
> of one bulb reduces the current drain more on a 68, because there are only
> two rear turn signal bulbs per side.    The drop in current from the loss
of
> one bulb is nearly 30% on a 68, apparently enough to totally stop the
> flashing.  (The little bulbs in the indicators hardly count, as they use
so
> little current, and the cornering light is on a different circuit.)
>
> I note in passing that those of us with the more luxurious and elegant
67's
> may not have this worry, as we have 3, yes that is three per side on the
> rear,
> thus the loss of a paltry single bulb reduces the current by only around
> 20%!
>
> In the case of flashers of the type which are not load sensitive, the
> heating
> current is provided by a separate internal circuit path which is not
> affected by the number of bulbs - these are usually referred to as "heavy
> duty" flashers.
>
> Dick Benjamin
>
>
>