[s-cars] Headlamp relay wiring weirdness - Insight needed

Franco Barber feb at febsun.cmhnet.org
Mon Feb 6 14:19:19 EST 2006

On Mon, Feb 06, 2006 at 01:37:18PM -0500, Dave Ellis wrote:
>      "Fred Munro in one of his posts (UrS4 Euro Light
>       Hi Beam Relay "Latch-on" Fix of Sat, 8 Jan 2000
>       08:38:46 -0500) described the problem associated
>       with the Highs not turning OFF in the relayed
>       Euro lights."
> Unfortunately I've been unable to locate a copy of that post.  If anyone 
> has a copy of the thread or a pointer to an archived location I'd much 
> appreciate it.
> Thanks!
> -Dave

Here's a copy of that post.
This is from my own archives of the main quattro list,
not the s-car list.  (Note please that my copies of that era are of
the digest version, so I don't have most of the original headers.)


Date: Sat, 8 Jan 2000 08:38:46 -0500
From: "Fred Munro" <munrof at isys.ca>
Subject: UrS4 Euro Light Hi Beam Relay "Latch-on" Fix

    I've gone through the Bentley wiring diagram, tested the system on my S4
and think I've found the problem causing the high beam relays to latch on.
I've come up with a couple of fixes, but haven't field tested them yet -
thought I'd throw this out to the list for info and comment.

    When the stock high beam wiring is used to drive a pair of relays for
Eurolights on the UrS4, the relays will activate when high beam is first
selected and will remain on when low beam is selected. The relays will open
if the headlights are switched off, the fog light relay is removed, or the
stock wiring is removed from one relay and reconnected to one high beam

    The AE (Audi Engineers) have decreed that the fog lights will shut off
when high beams are selected. This is probably due to some obscure safety
legislation or concern about heat in the headlamp housing with 3 bulbs
illuminated. Since the S4 low beams are always on, even when high beams are
selected, the standard dimmer switch cannot be used to trip out J5, the fog
light relay . AE have come up with a rather elegant solution - the coil on
J5 (terminal 85) is grounded through the high beam bulbs. When the high
beams are switched on, terminal 85 gets 12 volts, the same as terminal 86 on
the other side of the coil, and the relay drops out, shutting off the fog
lights. Terminal 86 is only fed power when the headlight switch is fully on.
    Along comes a FAE (Feckless Audi Enthusiast) who installs a set of
Eurolights and relays the high beams to the alternator to get maximum
voltage, maximum lumens, and avoid frying the headlight switches with the
500w "off-road" bulbs he's installed. The stock high beam wiring is used to
trigger the relay coils in time honoured fashion. When the headlights are
turned on with low beam selected, all is well - the fogs work and the low
beams work. High beam is selected, and the relays activate, turning on the
high beams and temporarily blinding the FAE with reflection off the garage
walls. Low beam is selected but the high beams stay on. Once the FAE becomes
aware this is not an image burned into his retinas, he finds it is because
the relay J5 coil is now grounded through the high beam relay coils and is
passing enough current to keep the high beam relays closed. Pulling the J5
relay or shutting off the headlights interrupts the power flow and lets the
high beam relays open. Reconnecting the stock high beam wiring to one bulb
grounds J5 through the lower resistance of the bulb and allows one high beam
relay to work properly.


    I've come up with two fixes, one which retains the current system
functionality and a cheaper, easier one which doesn't.
    The "Cheap Fix" is to remove the female terminal 85 from the relay J5
socket and insulate it with a piece of shrink tubing. Install another female
terminal into the socket and run it to ground. This will give you fog lights
whenever the headlight switch is "on", even when high beam is selected. You,
the aware and in-control Audi driver, will have to remember to turn them off
when you flip on the highs. Since high beams are not too useful in fog, this
may not be a great hardship.
    The "Good and Proper Fix" is to install an additional NC relay in the
circuit. As above, remove the female terminal 85 from the J5 socket and run
it to terminal 86 on the new relay. Install a new female terminal in the J5
socket and wire it to terminal 30 on the new relay. Wire terminals 85 and 87
on the new relay to ground. Now when low beams are on, the J5 coil is
grounded and J5 closes, powering the fog light switches. When the high beams
are selected, the new relay opens, interrupting the ground circuit on the J5
coil, causing J5 to open and shut off the fog lights.
    The new relay could be wired into terminal 86 of J5, but terminal 85 has
to come off anyway and this makes relaying the ground circuit a bit less

    I haven't field tested the fix yet, but since I love complex engineering
solutions  (why else would I own an Audi?) I plan to try the "Good and
Proper Fix" today if I can find a relay socket at a local wreckers. I plan
to install the new relay in a blank space in the main relay box under the
hood. I'll post the list on the outcome.

Fred Munro
'94 S4  96k km


Hope that was the right one.

Franco Barber                   feb at febsun.cmhnet.org
95 A6Q w/Gamma CD mit RDS!      Columbus, Ohio  USA
95 A6Q 5spd w/HCB-30 bluetooth car kit!

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