RE: rapid-fire turn signals

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

> >I actually use this same concept to cause my corner marker lights to
> flash
> >with the signals and still come on with the headlights ...
> 
> How would you actually wire that? The marker lights on my 
> Caprices are apparently wired like that, but all the wiring is
> too well-wrapped to tell what's connected where.
> 
The way that I did it was to wire the "ground" wire from the marker lamp to
the "hot" wire on the turn signal.  I'll describe how it works in a bit, but
what happens is that when the turn signals are off the marker light works
much as it did originally, on and off with the parking lights.  When the
turn signals are activated the marker light will flash ... if the parking
lights are off the marker will be illuminated when the turn signals are on,
and when the parking lights are on the marker light is illuminated when the
turn signals are off.  

The basic theory behind this approach is that the light is actually powered
and grounded in a way from each terminal on the bulb.  When the parking
lights are on the wire provided by Audi is supplied with something
approximating 12 volts :), and when the parking lights are off the
extinguished parking light bulbs provide a relatively low resistance path to
ground.  The new wiring configuration to the former ground on the marker
light will provide +12v when the turn signals are illuminated, and a
relatively low resistance to ground through the extinguished front and rear
turn signal bulbs when they're off.  Remember that the marker light will be
off when the voltage across its terminals is -0- ... it has no way of
knowing whether the actual applied voltage to both terminals is ground or 12
volts; this is the fact that allows the marker to flash when the parking
lights and turn signals are both running.  Notice that I used the term
"relatively low resistance to ground" a couple of times before ... the other
characteristic that this idea depends upon is that the marker lights are
fairly low wattage (and therefore relatively higher resistance) and there
are at least two other higher wattage bulbs (i.e. lower resistance) in the
path to ground.  What this does is to set up a resistive voltage divider
from the source of the 12v, through the marker light AND through the
unpowered lower resistance bulbs to ground.  The result of this voltage
divider is that there will be some voltage dropped across the unpowered lamp
filaments; therefore the marker lamp will not illuminate as brightly as it
did when it was really grounded and only came on with the parking lights.
You might also notice if you looked very closely that the unpowered
filaments are glowing very dimly as well.  

Huw sent me a message stating that he has relayed his marker lights to cause
them to flash ... seems to me that this would mean you'd need to add two
relays and some additional wiring to do this ... while it does provide full
voltage to the marker in all situations I tend to prefer the simple
approach.  In any event, if someone else would prefer to use relays, the way
to do this would be in effect to wire the relay's coil in exactly the same
way as I wired the bulb.  You would provide a fused +12v source to the relay
contacts (from the alternator of course, to provide the minimum voltage drop
:), connect the N.O. contact from the relay to the bulb lead that used to be
connected to the parking light circuit and leave the grounded terminal as
is.  Actually, to minimize the chance of accidentally shorting out the 12v
source, I would connect the +12v to the N.O. contact on the relay and the
bulb lead to the common ...

... given the amount of detail I ended up providing I think I'll post this
back to the list as well ...

HTH!
Steve Buchholz
San Jose, CA (USA)