euro lights/ecodes - long and nerdy - and post warning

Fri May 31 13:48:57 EDT 2002

Comments inserted.  Maybe a redirect of the thread should be nerding euros...

In a message dated 5/29/02 12:18:41 PM Central Daylight Time, Djdawson2

>OK, I'm not looking for trouble here but... SJ says:
Trouble?  Nope, but maybe too much information will come your way  :)

>Isn't a great deal of this car's wiring (and relays) an "outside install"...
my fuse box >is under the hood, and it contains a handful of relays.  Was
this a mistake on >Audi's part, or could we achieve similar good results by
installing well protected >relays for our headlights in the engine

Audi put the fuse block under the hood, after the fiascos with the ceramic
fuses/blocks.  It was 'another' mistake.  For more look how the later S cars
are done.  Some relays are under a watertight compartment that are exposed to
little in terms of elements.  Still, if you look at relay failure, those ones
under/in the dash fair better than those in the block under the hood.  I know
I have several original operating relays in my urq, that's 18years.  I've
done at least 3 FPR on my t44 alone.

>How does the starter provide such a current fluctuation?  I'm not in the
habit of >starting my car with the headlights on, but even if I did, that
circuit goes dead >upon starter activation... on any German car I've ever
owned.  Hit the starter, lights >go off, release and they're back on.  This,
to me, would appear no more harmful >than turning them on and off.

Dave, try hooking up a voltage meter to the battery post when you start the
car.  The BEST time to turn on the lights is after the car is running.  In
the scenario above, you have a 9/10volt hit, then a 13.8/14.45 (better said:
max alt output)  hit on a bulb designed for a 12.8 constant voltage.

>We're not talking about using the alternator line here.

Sure you are.   Try measuring the voltage at the battery post, and at the
jumper post.  Then load the alt with the car running.  IME, the voltage
measure is never the same.

>We're talking about using a >very heavy gauge feed.  I'm hoping that you're
not >suggesting that the jump post is >somehow not directly connected to the
battery, >and taking advantage of its >capacity (yes, via a post on the
starter... but we just >eliminated that as a possible >source for current
>I'm suggesting that you already have a direct run >from the battery to the
jump >post that consists of 2 sections of wire connected >together on the
starter post.  >I'm also certain of the fact that the headlight circuit >is
deactivated during starter >use, which eliminates the starter as a factor

Not really, see above.  All power is deactivated only until the ignition
switch springs to the on position.  IOW "deactivation" is only a temporary
thing Dave.  It's the "after-activation" voltage spikes that creates
problems.  Again, this is a known entity, the offroad guys have been down
this avenue for years.

> assuming that you use the original headlight wiring as the means to trip
your euro >light relays.  With these 2 things in mind, the only issue that
remains is relay >life/performance.  I believe it is possible to protect the
relays adequately within the >engine compartment.  What else is really left?

"Adequately?"  Ok.  14 guage wire is also "adequate".    As a shop dude,
adequate means I do it over again.  Just sharing some BTDT.

>Wiring runs... I believe you could accomplish the "post" type of install
using 1/3 of >the wire length required to go the other route.  In a low
voltage/high current >application, there are benefits to keeping those runs
as short as possible.

A 10guage feed is more than "adequate" for the longest of audi strings of 2
lights (see previous posts).  12 guage from the relay to the lights should be
considered min.

>But, I would have a hard time justifying running a high capacity line from
the >battery forward when one already exists.

The one that exists is a POS Dave.  Ck Mockry's site.  A high capacity line
from the alt to the battery direct takes about 1.5 hour (2 max).  And you
will find all sorts of good things from it (measure before and after A/C head
voltage - IME a good .6v increase is usually the average).  A good macguyver
is to snip the existing starter/battery run, and use it for your relay feed
wire (put a connector on it, you can put ALL light relays to that single
feed) - and it's already strung PERFECTLY from the battery.  There's a bunch
of room in the glove box area to put relays, btdt.

>And I'd personally have a hard time justifying the time and effort required
to keep >$8 relays inside my car.

IME, what happens with many of my customers is that when these eurolight
strings fail, it's usually not at a very good moment.  Peace of mind comes
from the set and forget method.  'In car' relays will do that.

 Fluctuating voltage is a bad thing.  For more try the FAQ at
(supplier of a myriad of halogen bulbs).

"How can you prevent overvoltage? The lamp should never operate beyond 8% of
the total rated voltage. Check that the power supply or line voltage is not
delivering spikes or surges to the lamp. It may be necessary to place in-line
suppressors in your system. Inspect your sockets periodically. Bad
connections will cause arcing which may surge the lamp. Avoid the use of
dimmers that may drive your lamp over the rated voltage. Finally, avoid any
unnecessary vibrations. "

Some knowns in the automotive industry:
halogen bulbs (actually any automotive bulb) are rated at xx watts at

12.8 x 8% = 1.0v

WRT to the comment about feed voltage not spiking speaks for itself.  The
alternator feed is the highest fluctuation voltage in any automotive
application.  Batteries make great capacitors (read: in-line suppressors).

Over the years, I seen/service/installed a plethora of "light" relay installs
(including the Audisport S2 rally car -relays in car).  Without question, the
better relay install is "in car".  Will "under hood" work?  Sure.  I'd sure
advocate that using the jumper post for the "feed" voltage is only
"convenient", not intended nor recommended for any relay feeds.

***IMPORTANT TO NOTE***  IF you do use the jumper post for your relay feed
starts (especially the AAA type) are 200+amps, do know that can easily short
(arc weld) the relays in the on position, and/or blow all bulbs immediately.

HTH and my .02

Scott Justusson
aka eur o nerd

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