[s-cars] Revisited: UrS4 Euro High Beam Relay "Latch-on" Fix

[Fred Munro]

Interesting observation, Wayne. I've only worked on my Canadian S4, so I
wasn't aware the US cars were wired differently. I don't think the Canadian
fog relay wiring has anything to do with the DRLs - I do think someone
decided the fog lights should not be on with the high beams and the wiring
was set up to make this so. It may be a Canadian regulation that I'm not
aware of.
If your latching is intermittent, it does make it difficult to find the
problem. Are you running one relay for both high beams or a relay for each
light?

Fred

-----Original Message-----
From: s-car-list-admin at audifans.com
[mailto:s-car-list-admin at audifans.com]On Behalf Of Wayne Dohnal
Sent: December 31, 2002 2:13 PM
To: S-car list; Fred Munro
Subject: [s-cars] Revisited: UrS4 Euro High Beam Relay "Latch-on" Fix


Portion of 2-week-old post for context:

>.....the fog light relay coil grounds through
>the high beam bulbs. When you relay the high beams, the fog light relay now
>grounds through the high beam relay coils because you've naturally used the
>high beam wires to drive the new relays. Once you activate the high beam
>relays, the fog light relay coil passes enough current to keep the HB
relays
>closed, even after you switch the high beams off. This depends on the
relays
>installed - some relays have a higher drop-out voltage and don't cause a
>"latching" problem.

There was a long thread on this subject, and I don't remember anyone
mentioning that this information applies to Canadian cars only.  The
American UrS4s are wired differently, with the '85' terminal of the fog
light relay being hardwired to ground.  I'd guess that the Canadian cars
ended up with their 'interesting' wiring scheme when the daytime running
lights were added after not having been originally designed in.

I was following the thread because my relayed high beams occasionally latch
on, and now I'm back to suspecting a sticky relay or headlight switch.  It's
hard to isolate because it only happens to me once every 2 months or so.

Wayne Dohnal
1994 S4

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