Fuse for brake lights keeps blowing - tech can't find problem

It's a 1998 A4 1.8 Quattro. First, they thought it was the switch, so
they replaced that. Test drive was fine. Next day, blown fuse.

Yesterday they spent 3 hours ($$) examining the wiring. Couldn't find
anything wrong. New fuse in, test drive was great. Today, blown fuse. I
replaced it, drove around, tried everything I could think of to make it
blow (turn indicators, power locks, stereo, A/C). Working great, but I
know I've got about 24 hours before it goes.

If anyone has a suggestion, I would greatly appreciate it. I'm at the
end of my tether. The only solution the service dept has (re-wiring)
is so horrifically complicated and expensive that even they don't want
to do it.

The only other issue I'm having, but this has been going on for many
months -- long before the brake light problem -- is the cruise control.
It works about 60% of the time. The rest of the time it won't engage,
or engages for a short period and then cuts off. Temperature and rain
don't seem to play a role. Happens in the dead of winter and during hot
summer days. I can live without it for now. (I mention it only in
case it's relevant.) But brake lights are serious. I actually found
out I had the problem by having a very angry motorist yell at me.

Please help!

If it's relevant, I live in a climate where the winters are very cold
(-40C is common) and the summers can be very hot and humid.

Thanks!

auto or manual?
the auto trans may have a solenoid or relay that needs that brake light
switch to allow you to select a driving range.

just a wild guess but did that tech check the wiring at the trunk lid? the
earlier Audis had problems with that wiring area breaking and causing fuses
to blow

might even be a bad or incorrect bulb

does anything else not work when that fuse blows?

the cruise control might be a bad switch at the pedal(s)

jmho
--
later,
dave
(One out of many daves)

> wrote in message
ups.com...
> It's a 1998 A4 1.8 Quattro. First, they thought it was the switch, so
> they replaced that. Test drive was fine. Next day, blown fuse.
>
> Yesterday they spent 3 hours ($$) examining the wiring. Couldn't find
> anything wrong. New fuse in, test drive was great. Today, blown fuse. I
> replaced it, drove around, tried everything I could think of to make it
> blow (turn indicators, power locks, stereo, A/C). Working great, but I
> know I've got about 24 hours before it goes.
>
> If anyone has a suggestion, I would greatly appreciate it. I'm at the
> end of my tether. The only solution the service dept has (re-wiring)
> is so horrifically complicated and expensive that even they don't want
> to do it.
>
> The only other issue I'm having, but this has been going on for many
> months -- long before the brake light problem -- is the cruise control.
> It works about 60% of the time. The rest of the time it won't engage,
> or engages for a short period and then cuts off. Temperature and rain
> don't seem to play a role. Happens in the dead of winter and during hot
> summer days. I can live without it for now. (I mention it only in
> case it's relevant.) But brake lights are serious. I actually found
> out I had the problem by having a very angry motorist yell at me.
>
> Please help!
>
> If it's relevant, I live in a climate where the winters are very cold
> (-40C is common) and the summers can be very hot and humid.
>
> Thanks!
>

On 16 Sep 2006 15:46:27 -0700, wrote:

>It's a 1998 A4 1.8 Quattro. First, they thought it was the switch, so
>they replaced that. Test drive was fine. Next day, blown fuse.
>
>Yesterday they spent 3 hours ($$) examining the wiring. Couldn't find
>anything wrong. New fuse in, test drive was great. Today, blown fuse. I
>replaced it, drove around, tried everything I could think of to make it
>blow (turn indicators, power locks, stereo, A/C). Working great, but I
>know I've got about 24 hours before it goes.

I once had a similar problem, many years ago, in a non-Audi car. I
discovered it when I was stopped by the police one night for driving
without tail lights.

The problem in that case turned out to be a wire that was chafing on
the metal part to which it was attached and, once the insulation had
worn through, was shorting. On that occasion the actual wire in
question was not on the tail lights circuit, but something else that
was fed through the same fuse. If you have the same problem - and I
hope you don't - it will be a real pig to trace.

Peter.

One out of many Daves wrote:
> auto or manual?

Manual.

> just a wild guess but did that tech check the wiring at the trunk lid?

They said they checked all the wiring "at the back"? Exact wording on
the bill:
"Looked at trunk area and under dash for source of malfunction.
Repositioned wires to try and recreate fuse blowing."

> might even be a bad or incorrect bulb
>
> does anything else not work when that fuse blows?
>
I haven't noticed anything else not working, although I've been
looking. I wish I knew out what else would be on that circuit, because
it might indeed be that (other) thing causing the fuse to blow. If they
haven't already, I'll tell the repair shop to replaced all of the
bulbs--see if that makes a difference.

Peter wrote:
> I once had a similar problem, many years ago, in a non-Audi car. I
>
> The problem in that case turned out to be a wire that was chafing on
> the metal part to which it was attached and, once the insulation had
> worn through, was shorting. On that occasion the actual wire in
> question was not on the tail lights circuit, but something else that
> was fed through the same fuse. If you have the same problem - and I
> hope you don't - it will be a real pig to trace.

That's precisely what I'm afraid of too.

I'm driving now with the cover for the third (middle) brake light
removed so that I can see in the rearview if the brake lights are
working. My guess is I'll be replacing the fuse sometime later today.
:-(

hmmm does your cigarette lighter work when the fuse blows?
I agree with Peter, I am thinking that maybe something else is blowing it.
Maybe something that always gets power like interior lights, trunk lights
maybe, etc. I knew an Audi 5000 that had a vanity light that would drain
the battery down even though the bulb did not light up with the ign. off.

OK test out other components to see if they work now. Your owner's manual
should tell you what that fuse protects.
You might want to take that fuse out and test your other components. But I
guess in time the fuse will blow and THEN you can test things to see what
else does not work. ;-)

don't throw in new bulbs, but YOU can possibly inspect them. ;-)
but I would think that the dealer tech checked them. 8^o

Here's the latest:

Driving to work this morning, kept looking at the middle brake light
(cap is off) every time I braked. Just before I got on the freeway,
about 20 minutes into my trip, I braked at a light. No brake lights. I
was doing nothing else at the time -- no turn signal, nada, just
driving.

So....I took it to a different service place, one that I had used many
times before. They just called me. After three hours labour, their
diagnosis is...they can't find the problem. It is to weep....

Told the tech to replace all the bulbs in the rear (what the heck--he
figured it couldn't hurt). The tech is going to drive it home and back
tonight, see if he can get it to blow. Everyone says they have to "see
it" happen to figure it out. Please god, let it blow.

I mentioned the (pre-existing) problem with the cruise (which is turned
off, and has been off for a while). He said maybe we should fix that,
see if it's related. What do you think? He mentioned replacing a
"module" for the cruise (sorry, no idea what means).

Sigh.

have him disconnect the cruise module if possible. Maybe the module is
blowing that fuse if it is tied to the brake light switch.


> wrote in message
oups.com...
> Here's the latest:
>
> Driving to work this morning, kept looking at the middle brake light
> (cap is off) every time I braked. Just before I got on the freeway,
> about 20 minutes into my trip, I braked at a light. No brake lights. I
> was doing nothing else at the time -- no turn signal, nada, just
> driving.
>
> So....I took it to a different service place, one that I had used many
> times before. They just called me. After three hours labour, their
> diagnosis is...they can't find the problem. It is to weep....
>
> Told the tech to replace all the bulbs in the rear (what the heck--he
> figured it couldn't hurt). The tech is going to drive it home and back
> tonight, see if he can get it to blow. Everyone says they have to "see
> it" happen to figure it out. Please god, let it blow.
>
> I mentioned the (pre-existing) problem with the cruise (which is turned
> off, and has been off for a while). He said maybe we should fix that,
> see if it's related. What do you think? He mentioned replacing a
> "module" for the cruise (sorry, no idea what means).
>
> Sigh.
>
>