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Re: 2004 R1100S Fuses

Hello Paige,

From: <plpklt@xxxxxxx>

WRT: "I think the R11s must have the worst electrical system
   ever put on a beemer. My son melted the entire back
   section of wiring down."


> I understand what you are saying and greatly respect your point.
> I too like to fully examine and explore issues in hopefully an
> open minded way.  I also love a good debate and a good debater.
> My point is that on the R11S, what I found was very light gauge wiring
> with thin insulation.  I think that on the r11S they were trying to save
> weight in anyway they could.  I think they just lightened the wiring up
> too much.  Bmw doesn't use very heavy wiring anyway (based on my 96RT)
> but I understand that short runs of wire don't need to be heavy when the
> proper loads are considered.

While I concur that it appears BMW used "thin gauge" wire and "thin
insulation" (based on visual inspection only), I cannot comment in the
following areas:

 o Why BMW chose to do so. You speculate that they may have tried
   to save weight. It is equally feasible speculation that from an
   engineering perspective, heavier wiring was not required.

 o I cannot provide a genuine comparative analysis between the wire
   used on an R1100S and other models. Is it thinner? By how much?
   On all wires, or on select wired?

Due to the lack of quantitative or qualitative metrics, I feel it is
reasonable to steer clear of statements that would imply, or lead the reader
to conclude, that BMW "cut corners" or "skimped" on the wiring in some way.

> One can well make the argument that If my son had  not tried to add
> anything, the bike probably would have been fine, but what he added was
> LED's which it is hard to imagine they  would overload the circuit,
> especially since most of the lights were brake lights which would have
> only been on a few seconds at a time, as opposed to a constant load.
> Led's loads are measured in Milli-amps.

My preference is to clearly identify what is genuinely known (and can be
validated as being factual) as opposed to that which is speculative (e.g.,
"I *believe* that X has occurred, though I am not certain.") See my comments 
below for more details.

> I also don't know exactly what he did and how, but I know he would have
> followed any directions that came with the hyper lights which are
> ususally pretty straight forward ( he reads the directions, I never do
> until the fire starts)....

So allow me to restate the facts as we know them. Please correct me where I
have erred:

1) Your son attempted to install LED-style lights on his BMW R1100S

2) We *believe* he read and understood the instructions, and that he
   followed them to the letter.

3) He experienced a problem in which some of the BMW wiring
   harness, or stock BMW wires, "melted".

Here are things that we don't know with absolute certainty:

1) What is the *actual* current draw of the lights? Are we certain
   that this current draw + the current draw of existing systems -
   current draw of systems that were replaced <= recommended

2) Were the lights confirmed to be working an in good order, and
   free of defects before installation was attempted? (a possible cause
   of the problem)

3) Were the instructions provided with the lights detailed, and specific
   to the R1100S?  I speculate that they were generic, and depended
   upon the installer's knowledge of the target vehicle's electrical
   system for proper installation. (Another possible cause of the

4) Was the motorcycle stock, or had it been modified in any manner
   prior to the problem arising? Prior modifications to the electrical
   system, or other systems, could have unknowingly introduced issues.
   Ditto with undiscovered wear (as an extreme example, I would not
   be surprised if a bike with 300,000 miles on the clock had an
   electrical issue due to wear on wiring from flexing and/or vibrations).

5) Was the intended installation conceptually correct? Were
   appropriate sources for a "power" wire and grounding identified?
   (Another possible cause of the problem).

6) Was the installation carried out without incident or error? For
   example, a "power" wire may have come in contact with a ground
   point and shorted out.

7) Was the installed system or its components damaged in any way
   during installation? For example, a "power" wire may have come in
   contact with a ground source.

The items I have listed above all leave significant doubt about the cause of
the issue, and all of them are more likely to be the cause than a faulty
electrical system design or suboptimal implementation of that design by BMW.
We do know from abundant past experience that R1100Ses can be
augmented with additional electrical gadgets (horns, lights, GPS, CB,
Intercom, multiple power sockets for heated clothing, etc), and experience
no issues. The fact that it has been done so many times without problems
strongly suggests that it is *not* the R1100S's electrical system that is
extremely intolerant to modifications, but rather, that the issue lies
somewhere else.

> One other thing is that the bike only has 4 fuses ( If I remember
> correctly)  which tells me that they are not protectecting each circuit
> with a fuse, as you would do in a building....

The practice of having multiple items protected by one fuse are common in
motorcycles, automobiles, and buildings. In buildings, for example, you will
typically find several wall outlets and light fixtures protected by a single

>... When you try to protect
> multimple circuits with a single fuse, how do you size the fuse
> correctly?

In the case of a motorcycle, you follow the manufacturer's recommended fuse
rating, both in terms of amperage and fuse type (e.g., 10 amp "slow blow").
If you are designing a circuit yourself, or modifying an existing circuit,
that's a different story, and it is more suitable for its own thread.

> Ideally a fuse should be designed to blow at 80% of the capacity of the
> smallest wire.  If two wires melt together the capactiy of the wire is
> greatly increased, hence melt down.  The old slash 5 only had two fuses,
> but it had wiring the size of house wiring.  One fuse was used for the
> ignition , the other for the lighting, If you lost the lighting fuse you
> could atleast ride it home (perhaps in the dark).
> I therefore would contend..... the bike is not properly fused, probably
> the root problem...

I believe the points I have made provide sufficient doubt for that
assertion. We do know that the wiring and fusing on the R1100S is different
that on the "slash 5", but so far, we have no evidence that it is "not
properly fused".

> The wiring is sized only for the orignal design loads...

This, I believe, is an unsupported speculation. Please provide proof of this
if you have it.

> ...which is technically correct but we all know there isn't a beemer
> around that doesn't have a little doo-dad added, usually there is a little
> safety factor built into any design to allow a little cushion.
> It is up to the designer to make these decisions, but a wise designer
> makes allowances for "field" conditons, these occurences that are likely
> to happen.

Again, I believe we have no proof to support this belief, and therefore, we
don't have any ammunition to assert that the R1100S's electrical system is
suboptimal for the stock bike + "reasonably expected modifications." On the
contrary, there is a lot of anecdotal evidence that suggests the R1100S is
quite capable of supporting additional electrical load due to non-stock and
non-BMW accessories, without incident.

> They also bundle the wires tightly with that cloth electrical tape.  This
> doesn't allow the wiring to disipate any excess heat.

To the best of my knowledge, we don't have any proof that the wiring *needs* 
to dissipate any excess heat, so this observation is moot.

> Is it a design fault? or just circumstances?  If you can anticipate a
> problem and do nothing to avoid it I conclude it is a desgin flaw, even
> if it is a passive fault.   That is how they treat it in my profession
> (architect).

Then as an architect, you likely know that you face numerous constraints,
such as the physical space in which your design must exist (packaging),
costs, delivery schedule, aesthetics, etc.

My experience is that when things are designed, some sharp minds try to
anticipate the "risks" that may arise, the probability of those risks
becoming an issue, and an appropriate way to mitigate or negate those risks.
In doing so, all sorts of other issues come into play such as packaging,
practicality, cost, etc. For example, a motorcycle helmet that is 2 feet
thick would provide dramatically more protection to the wearer in the event
of an impact than today's helmets, but in doing so, it would no longer be
wearable. Similarly, aircraft could be designed to be much more survivable
in the event of an crash, but the penalty would be increased weight which
means a significantly reduced payload, which would result in passenger
airfare becoming prohibitively expensive. Even bridges are affected -- They
are *not* designed to "not fall down", but rather, they are designed to
withstand specific anticipated loads under specific ambient conditions.

To bring this back to the world of BMW bikes, and more specifically, the
R1100S's electrical wiring, I believe you and I don't have any hard facts
about the built-in "margin of safety" that is offered by the stock wiring.
As such, it is prudent not to speculate what they may be. We do know,
however, that many, many people have modified their R1100Ses' wiring in some
way and not had issues. If you want more anecdotal evidence of this, post a
message to this list and to IBMWR asking people for their stories. I am one
of these folks.

In short, I believe we have fallen well short of meeting the burden of proof 
to establish that the cause of your melted wires is a suboptimal electrical 
system design in your R1100S motorcycle.

> So what about it? did I make a case for  my rash statement?

I understand why you hold your position, though I do not agree with it. I 
hope that my "alternate perspective" shows how

- -Steve Makohin
 '01 R1100S/ABS
 Oakville, Ontario, Canada