[ba] relay bypass system for headlights

Buchholz, Steven Steven.Buchholz at kla-tencor.com
Wed Feb 6 21:23:06 EST 2002

... for an older Audi there really isn't that much to it ... but it can get
a bit complicated if you have a car that has the headlight monitors and you
want them to continue to let you know when a bulb is blown.

To my mind the main issue is that things are best if you can isolate the
relays from the environment under the hood.  I have found that it is fairly
easy to find ABS controller boxes for cheap ... it is best if you find them
yourself at the wrecking yard because you're going to want the mating
connector as well.  These boxes are sealed and have high power pins.  I
found that it is possible to find Audi relays which are SPST and have a 70A
contact rating (!) ... a couple of these and you are good to go.  I have yet
to find a solution I really like for fusing ... I usually go to Radio Shaft
and buy a fuse panel that holds 4 3AG (AGC) fuses.  I'd really like to find
some way to use the blade style fuses ... but I've never seen a fuse panel
available for them.  Some people like to use relays to do the "marker flash"
mod ... to do this you would need two more relays (personally I find
relocating the ground on the markers to the hot on the adjacent signal to be
more than adequate).  If you want to use the bulb out detector module that
will add one more "relay" to the box ... all you need is a single low
current wire back to the instrument cluster to make the warning work with
the remote monitor.  I've never tried to cram all this in one box ... but I
did fit all but the marker flash into an ABS box for the euro lights for my
'88 5kCSQ Avant.

Steve Buchholz
San Jose, CA (USA)
> Then I came across this site and it got me thinking about a
> relay bypass for
> my Coupe.
> I worked from the schematic on this page.

The site seems moribund and the writer seemed to have an axe to grind at the
time about any bulbs that weren't standard. But the relay stuff is good.

These guys offer a ready made harness for $99. For some reason they list it
on other pages for $119 so there might be 2 different ones.


There is a step by step howto on Huw's site. Huw's is possibly the most
useful website I've ever found. Ton 'a work he's done on that site.


I would get the Hella relays with the integral fuses if I was doing it
again. It would simplify things quite a bit.


This site has good info on lighting. Unfortunately much better than the USA
Hella site but then fortunately we have this thing called the Internet that
allows us to get to it. I hope to go to the Xenon lamp/bulb setup when funds
permit. Poke around, they have good background info on relays and the loss
of light output vs. voltage drops.


I had to remove the outer lamps to get the connectors onto the sealed beams
as it was too tight internally. I would recommend that if you have to do
this also then you take that opportunity to center the lamps in their
holders and center the adjustment screws in their runs (and spray some WD-40
on the screws) as you may have had your lights misadjusted and not known it
due to the poor light output. When you get back to 100% output it is very
apparent if your lights are off and having them ready to adjust properly
will save the second trip in to get them centered.

I now have better lighting than I've had for at least the last 12 years.



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