Internal lights fuse problem

My father has a 1994 E34/M50 that keeps blowing the fuse for the
internal lights. It seemed as if the problem was with the switch for
the trunk lid, but it doesn't appear that's the case. Apparently
there's a short somewhere, but we're having trouble tracking it down.
Here's what has happened:

He would go to the gym, open the trunk, take out his bag and all was
well. The trunk light would work. Close the trunk, go into the gym,
come out, open the trunk and the light wasn't working. Fuse blown.
This has happened several times. Yeah, we know, if the fuse keeps
blowing, then something's doing it for a reason. But he's been letting
this happen to try to diagnose the problem. (He's not stupid with this
as he's an electrical engineer by trade.) He's tried moving around the
wire harness around the trunk hinge to reproduce the problem, but no dice.

Since the problem seemed to be associated with opening and closing the
trunk he disconnected the trunk switch for the light to see if the
problem was with the switch itself. Fuse still blows. So that's not
the problem.

The latest experiment involved locking the car and then pulling on the
driver's door to turn on the interior lights. (Trunk switch is still
disconnected.) Lights turn on then eventually fade out as they're
supposed to. He does this three or four times and things work fine.
The next time he does it, the lights don't turn on. Fuse is blown.

So the problem is elsewhere. He has a Bentley manual and has the wiring
diagrams to refer to, but he doesn't know where to start looking. Does
anybody know where the problem lies?

--
So you're a feminist...Isn't that cute

"Voinin" > wrote in message
...
> My father has a 1994 E34/M50 that keeps blowing the fuse for the internal
> lights. It seemed as if the problem was with the switch for the trunk
> lid, but it doesn't appear that's the case. Apparently there's a short
> somewhere, but we're having trouble tracking it down. Here's what has
> happened:
>
> He would go to the gym, open the trunk, take out his bag and all was well.
> The trunk light would work. Close the trunk, go into the gym, come out,
> open the trunk and the light wasn't working. Fuse blown. This has
> happened several times. Yeah, we know, if the fuse keeps blowing, then
> something's doing it for a reason. But he's been letting this happen to
> try to diagnose the problem. (He's not stupid with this as he's an
> electrical engineer by trade.) He's tried moving around the wire harness
> around the trunk hinge to reproduce the problem, but no dice.
>
> Since the problem seemed to be associated with opening and closing the
> trunk he disconnected the trunk switch for the light to see if the problem
> was with the switch itself. Fuse still blows. So that's not the problem.
>
> The latest experiment involved locking the car and then pulling on the
> driver's door to turn on the interior lights. (Trunk switch is still
> disconnected.) Lights turn on then eventually fade out as they're
> supposed to. He does this three or four times and things work fine. The
> next time he does it, the lights don't turn on. Fuse is blown.
>
> So the problem is elsewhere. He has a Bentley manual and has the wiring
> diagrams to refer to, but he doesn't know where to start looking. Does
> anybody know where the problem lies?
>
> --
> So you're a feminist...Isn't that cute

so in short it's activated by the very slightest movement of the
car............gonna be a bugggger to track that one.

In article >,
Voinin > wrote:
> Since the problem seemed to be associated with opening and closing the
> trunk he disconnected the trunk switch for the light to see if the
> problem was with the switch itself. Fuse still blows. So that's not
> the problem.

Normally, the switch just completes a ground circuit so any fault in the
switch shouldn't result in a fuse blowing.

> The latest experiment involved locking the car and then pulling on the
> driver's door to turn on the interior lights. (Trunk switch is still
> disconnected.) Lights turn on then eventually fade out as they're
> supposed to. He does this three or four times and things work fine.
> The next time he does it, the lights don't turn on. Fuse is blown.

> So the problem is elsewhere. He has a Bentley manual and has the wiring
> diagrams to refer to, but he doesn't know where to start looking. Does
> anybody know where the problem lies?

I'd be inclined to look for a wiring fault where the loom goes to the boot
lid - insulation frayed through causing a short somewhere.

--
*Plagiarism saves time *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
> In article >,
> Voinin > wrote:
>> Since the problem seemed to be associated with opening and closing the
>> trunk he disconnected the trunk switch for the light to see if the
>> problem was with the switch itself. Fuse still blows. So that's not
>> the problem.
>
> Normally, the switch just completes a ground circuit so any fault in the
> switch shouldn't result in a fuse blowing.
>
>> The latest experiment involved locking the car and then pulling on the
>> driver's door to turn on the interior lights. (Trunk switch is still
>> disconnected.) Lights turn on then eventually fade out as they're
>> supposed to. He does this three or four times and things work fine.
>> The next time he does it, the lights don't turn on. Fuse is blown.
>
>> So the problem is elsewhere. He has a Bentley manual and has the wiring
>> diagrams to refer to, but he doesn't know where to start looking. Does
>> anybody know where the problem lies?
>
> I'd be inclined to look for a wiring fault where the loom goes to the boot
> lid - insulation frayed through causing a short somewhere.

Yeah, he has looked there and he hasn't seen anything positive. It's my
understanding that the manual doesn't show where the wiring is
positioned and I have a feeling that it's not exactly easy to reach.
While the Bentley is the best third party manual available, it's lacking
in many respects. I was kind of hoping somebody might have seen this
before or if this was a problem that somebody had a clue as to a
specific place to look other than where we've looked already or if
somebody knew the more likely places to look.

--
A banker is a fellow who lends you his umbrella when the sun is shining,
but wants it back the minute it begins to rain.
-- Mark Twain (1835-1910)

No, the switch doesn't complete the ground circuit. According to the
diagram, it is in the hot line and supplies 12V to the lamps.

The blown fuse is simply parted, no evidence of major current flow or of
any violent situation.

(This is the guy with the problem.)

And there is essentially NO movement of the car. The fuse blows with
the vehicle simply sitting quietly.

Bob

Bob wrote:
> No, the switch doesn't complete the ground circuit. According to the
> diagram, it is in the hot line and supplies 12V to the lamps.
>
> The blown fuse is simply parted, no evidence of major current flow or of
> any violent situation.
>
> (This is the guy with the problem.)
>
> And there is essentially NO movement of the car. The fuse blows with
> the vehicle simply sitting quietly.
>
> Bob

As Dave mentioned - a VERY common failure point for the boot-lid (trunk
lid) wiring is the section that connects the lid to the body of the car.
People have had cars catch fire because of failure of this section. The
fix is to open up the bundle of wires and find where the insulation has
worn through, then tape it up.. or replace that section of the harness.

In article <CShfg.11036$ho6.1210@trnddc07>,
Bob > wrote:
> No, the switch doesn't complete the ground circuit. According to the
> diagram, it is in the hot line and supplies 12V to the lamps.

I've not got a full diagram for the E34, but assumed it was the same as
the interior lights - and the door switches for those do just provide a
ground. However, it matters not if the problem still exists with the
switch disconnected.

> The blown fuse is simply parted, no evidence of major current flow or of
> any violent situation.

Right.

> (This is the guy with the problem.)

> And there is essentially NO movement of the car. The fuse blows with
> the vehicle simply sitting quietly.

If you have the circuit diagram you'll just need to check what else that
fuse feeds (if anything) and check all the wiring. It's still likely to be
a short somewhere - and this wouldn't necessarily show a 'violent'
situation due to the resistance of the cable run.

--
*Oh, what a tangled website we weave when first we practice *

Dave Plowman London SW
To e-mail, change noise into sound.

No, the switch is in the hot lead. The lamps go to ground. At least
the Bentley book says so.

I guess I'll pull apart the harness and look for trouble there. But I
am confounded because nothing touched the car and the fuse went. The
dome lights worked fine and then poof.

To make it more of a mystery, I reached up and flexed the harness quite
a bit before this latest fuse blowing and it felt fine. So maybe the
problem isn't in the part that flexes. I measured the current draw
while flexing the harness and there was no sign of an intermittent. So
if flexing it manually doesn't cause the short, why would it short while
sitting quietly?

There seems to be no other load on that fuse except one wire that says
it goes to the burglar alarm, which I don't have on my car.

Bob wrote:
> No, the switch is in the hot lead. The lamps go to ground. At least
> the Bentley book says so.
>
> I guess I'll pull apart the harness and look for trouble there. But I
> am confounded because nothing touched the car and the fuse went. The
> dome lights worked fine and then poof.
>
> To make it more of a mystery, I reached up and flexed the harness
> quite a bit before this latest fuse blowing and it felt fine. So
> maybe the problem isn't in the part that flexes. I measured the
> current draw while flexing the harness and there was no sign of an
> intermittent. So if flexing it manually doesn't cause the short, why
> would it short while sitting quietly?
>
> There seems to be no other load on that fuse except one wire that says
> it goes to the burglar alarm, which I don't have on my car.

Could there be some metallic debris in the fuse box? If the fuse box is in
the engine compartment, then there could be some slight movement due to the
engine cooling down or boot/door closure.

Andrew

Andrew Morton wrote:
> Bob wrote:
>> No, the switch is in the hot lead. The lamps go to ground. At least
>> the Bentley book says so.
>>
>> I guess I'll pull apart the harness and look for trouble there. But I
>> am confounded because nothing touched the car and the fuse went. The
>> dome lights worked fine and then poof.
>>
>> To make it more of a mystery, I reached up and flexed the harness
>> quite a bit before this latest fuse blowing and it felt fine. So
>> maybe the problem isn't in the part that flexes. I measured the
>> current draw while flexing the harness and there was no sign of an
>> intermittent. So if flexing it manually doesn't cause the short, why
>> would it short while sitting quietly?
>>
>> There seems to be no other load on that fuse except one wire that says
>> it goes to the burglar alarm, which I don't have on my car.
>
> Could there be some metallic debris in the fuse box? If the fuse box is in
> the engine compartment, then there could be some slight movement due to the
> engine cooling down or boot/door closure.
>
> Andrew
>
>
I don't think so. For instance, I can start with a good fuse, drive the
car around town or on the freeway, park it, come back and drive some
more. Then I leave the car for the night with everything just fine, and
in the morning the fuse is blown. Nobody near the car, no motion.

It's almost as if there is a timer somewhere that comes up and has a
short in it. It can go for days or weeks without trouble or it can blow
in a day. I sincerely believe that there is no correlation between the
motion of the car and the short.

One thing that has never happened - drive the car, shut it off, and fuse
blown. Never. Always when the car has been sitting by itself.

That's why I feel that tearing apart the harness won't yield the answer.