euro light relay question

[Fred Munro]

Hi Eric;

The problem with the relay set-up and the fog lights is the way Audi
grounded the fog light relay coil. It is grounded through the filament on
the high beam bulb, so when you turn on the high beams, the relay coil loses
it's ground, and the fog lights shut off. A very clever application, but it
screws up the high beam relay application since enough current can feed back
through the fog light relay coil to hold the high beam relays closed when
you flip the dimmer to "Low". Pulling the fog relay breaks this circuit and
allows the high beam relays to work properly. A fix is remove the existing
fog relay ground and  run a separate ground for the fog light relay coil to
T87 on a high beam relay - this again grounds the fog relay through the high
beam bulb, restoring the design intent.Some cars have this problem, and
apparently some don't - my S4 did.
Where are your relays mounted? If they are in the engine compartment, they
may be getting too hot in 120F ambient temperatures. Buzzing may indicate
insufficient voltage to activate the relay - have you measured the coil
voltage with both relays installed and buzzing?

HTH

Fred Munro
'94 S4  111k km

----- Original Message -----
From: "Harten Eric C Capt AWFC/TD" <Eric.Harten at nellis.af.mil>
To: "'quattro list'" <quattro at audifans.com>
Sent: Monday, September 11, 2000 6:22 PM
Subject: euro light relay question


> I have put relays into my 1995 90 for high-watt bulbs and eventual euro
> light conversion, but they have been doing some weird things lately.  I
did
> the standard thing with using the existing headlight sockets to power the
> relays.  All worked well at first.  The only problem I had was that since
> the fogs and high-beams used the same ground, I had to pull the fog relay
to
> let the high-beam relays shut off properly ( they had been sticking on due
> to a residual voltage).  Now, on what seems to only be hot days)  the
relays
> will not come on sometimes.  They just start to buzz.  During this
> condition, when I turn on my lights, the high-beam dash light comes on
very
> weak (no light and a buzz).  When I turn on the high's, the dash light
> brightens up a bit but still no light.  I then pulled the new high-beam
> relay and just left the low beam relay and I have not had a problem for a
> couple of weeks.  Have I developed a short?  But, why the apparent thermal
> effect?  Cooked relays in 120 deg heat?  Some ground I have not dealt
with?
> Each relay has it's own chassis ground.  I have checked all the pins with
a
> multi-meter and all the voltages checked out.  Any ideas?
>
> Eric
>
> 1995 90SQ
> 2001 A41.8T
>
>
>
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