BMW electrical problems.

Any BMW gurus out there?

I am having a completely frustrating electrical problem with my 1988
K100RS which is simply baffling me - so, as a last resort before
outlaying the vast amounts an auto electrician will likely cost me, I
thought I'd ask the collected wisdom if anyone had seen similar
problems.

After an indeterminate but varied period of riding, I get the following
symptoms.

1) Indicators stop working, or work erratically - for example, trying to
turn on the right hand indicator may result in both indicators flashing,
al-la hazard lights, or nothing flashing, or occasionally the LEFT
indicator flashing.

2) Horn doesn't work.

3) Headlight doesn't work

I can't see the tail/braoek light, as it always happens when I'm riding.

The bike, however, keeps running, and the engine seems fine. However, if
I stop the engine by stalling or turning it off {key or kill switch},
the starter motor will not turn over - I hear a loud whiring from under
the tank which I assume is the fuel pump or similar, but nothing from
the starter. I can, however, start the bike by bump starting it.

I have blown no fuses or bulbs recently, and when the stuff works it all
works perfectly.

My initial thought was that the battery had gone bad, so I eliminated
this as a suspect by the simple expedient of replacing it with a brand
new one. No joy.

I've looked at the circuit diagram fromt he Hayes manual until I'm blue
in the face and, beyond the battery, I can't see anything obvious that
would stop all the bits listed from working at the same time. It *seems*
to be related to heat somehow - the hotter the day, or the more
stop/start traffic I get stuck in, the quicker the problem occurs.

Has anyone come across this problem, or a problem with similar symptoms
before and could shed some light on which bit I should look at? Or do I
just bite the bullet & try to find an auto electrician to look at it for
me?

DaZZa

 

I'm guessing a bit, most of my experience is with boxer electrics.

I'd suspect an earthing problem. A dodgy connection might fail
intermittently in an unpredictable but heat/moisture-related way.
Probably in the way the instrument cluster/fairing/handlebar switches
are earthed. There is probably a single earth return point for the part
of the wiring harness that services the 'front' of the bike.

This would explain the haphazard indicators, horn and headlight. The
starting issue may be because one of the sensors that govern starting
(sidestand switch? clutch switch, gearbox switch? uses the same earth
return point.

In your wiring diagram, see if you can detect a likely candidate point,
then dive into the fairing/headlight area and look for a suspect
connection. You may need to pull apart, clean and replug a few
connectors. Do one at a time.

It may be the battery earth connection, but since the ignition and fuel
pump work, I doubt it.

BMW have a habit of making 'odd' earth return arrangements.

I think on some models, they can rely on a good electrical path through
the steering head. An earth bypass wire may be called for.

Have a look at the forum at http://www.motobins.com/

It has a good signal to noise ratio, and a population of BMW owners
skilled at diagnosing such difficulties.

Moike

 

In aus.motorcycles on 17 Feb 2005 02:04:59 GMT

My instant suspicion is a bad earth, track 'em all down and clean 'em
all up.

On a Guzzi, the startermotor no go is usually bad power to the relay or
less usually bad relay.

If you can't find it, try John at MotoCiclo in St Peters for electrical
work, if he can get Brit and Italian electrics working, German ones will
be nothing! 9557 7234. You are in Sydney or near to aren't you?

Zebee

 

city ?
I have a manual some where ( Im happy to say my k100 runs fine)
check the conectors , plugs tend to corrode

 

I concur with all previous advice. Fault will most likely be at a
termination ( earth points. indicators, plug connectors) or where isulation
has rubbed through. You will have to thoroughly inspect the wiring from
front to back. Be patient and take your time....have a play and leave it for
a while and come back to it, otherwise it will drive you nuts!!!
Cheaper for you to spend a few hours on it than pay an auto lecky......he
will just be doing the same thing anyway...
Stephen

 

have you got the trusty multi meter out as yet for investigations ??

that would be the 1st thing to be doing

 

With anything electrical (since a problem with a Fairlane), I pull out all
fuses & put them back, remove/unplug all relays & put them back, wriggle
everything that can be wriggled that looks electrical, and find the earth
and check that it's clean & tight.
Worked every time (except once). I can't get the light behind my odometer
to work on the EF Fairmont, and I'm too lousy to go to a sparky with such a
trivial thing.

 

snip

i think you might find that the light is a surface mount LED

 

LED?! That would be a "LIGHT emitting diode", I presume J5. It may still
be a diode, but it doesn't emit light, therefore it still doesn't work,
whatever I call it (or whatever you call it).

Having said that, do you have any idea what to do about it, or is your
repertoire restricted to identification?

 

Maybe it's DED
(Dark Emitting Diode)
Clem

 

snip

yep thats about it

it is prob a LED that is broken but of course it could just be a normal
globe

remove the intrument cluster and have a look if there is a globe to be
changed

I havent pulled one of those ford dash apart before but i am guessing it is
a LED based on the
fact that the EF has a digital odo

Surface mount LEDs are available at Jaycar or to have it done take the PCB
to a guy
that does mobile phones , you know the dodgy asian guys that change LEDs to
spanky blue
ones , provided that its an LED and could be changed easily

 

This might seem strange cause it did to me when the same happened.

It's the starter motor brushes, get them replaced. Quite common on a K100,
you can buy orig parts or most auto elecs can make brushes out of generic
parts.

Alan

 

Not saying I'd disbelieve you Al. I'd wager you've forgotten more than
I have about bimmers. But how on earth do starter motor brushes cause
the indicators to go feral?

Moike

 

I know they are all saying bad earth, and to a certain extent that is true
as many circuits on the K seem to rely on the starter for earth. But trust
me, just take the starter motor out and have a look at the brushes, it is
the problem. I've seen it already on two of the three K100s I've had(high
mileage both of 'em). The reason some of your electrics are fading in and
out is the worn brush making an intermittent contact with the armature, give
the bike a big rev and sometimes some of kicks back in momentarily(vibes).
There should be one long brush and one short brush, not even length. The
long one wears out first.

Al

 

Thats why it was such a confusing problem Moike, it doesn' make any sense at
all. They earth some circuits through the starter for some stupid reason,
that' why it has a particularly long brush on that side, it's sacrificial.
Like I said, it' happened to two of my own bikes, first time it drove me
nuts, I was chasing connections etc, then I tapped the starter with a
screwdriver and the lights came back on, that led me to further
investigation. Second time it happened, I knew straight away, but had to
stop on the central coast overnight due to no lights to get home.

Al

 

If you havnt pulled one apart why talk shit then?

Its a normal incandesant globe (plug in type) that backlights an LCD
display.

 

It's the starter motor brushes, get them replaced. Quite common on a

AAAHHH YES!!...that happened to me once

The reason behind it is that when the starter is turning there is no
earth through it for ancillary ccts...so headlights and stuff that you
don't want on while cranking the engine.....aren't

And when the brushes are worn enough for it to be a problem, the bike
won't go

I recall twas quite easy to fix, and not expensive...but an absolute
bugger of a thing to diagnose

Now, does anyone know about addressing the fast counter driver on a
Festo 640 PLC?

 

this is the internet its full of shit

easy fix then

 

Clamp a set of vice-grips on it just tight enough to slow it down. Be
careful, don't overdo it.

Moike

(festo what?)

 

no no no


you address it same as you would address a golf ball. Wearing funny pants(
and socks that only Pat would wear)