http://www.gumtree.com.au/s-ad/tanilba-bay/motorcycles/1983-bmw-k100-/1010387374#
first time I have ever seen this set up for fuel indicators, I'm guessing the second is relating to what is in reserve ?
can any one shed alight on this, just interested, was it specific to year/ country ?
A reasonable price for the condition, extras and low mileage Thanks Ed.

They had that through to end 85 or close. A 7ltr and 4ltr light to nag you.

Thanks Rick, I suppose better than an orange light that only tells you when you are in reserve.
Were the numbers all that accurate? (scrub that remark)
were they number dials or were they just lights that showed which zone you were in.... unlike myself I never know what zone I am in
my fuel needle wobbles all over the place , I try to gauge by the centre of the wobble, and it also seems to react strongly with the throttle , ie 1/4 to1/8 on acceleration, then return on release of the throttle.

The only acurate fuel gauge I have ever had was to look into the tank and gauge if it would get you to the next servo or not

The 4 & 7 L instrument (and sensor) was used up to 04/85.

And wasn`t that accurate, the 7 L lamp did start flashing at around half tank........
the circuit was then modified, the 7 L lamp left out and a delay function built in on the pcb to the 4 L lamp.

Then from 04/85 the thermistor sensor was removed, and a float sensor and a 5 L lamp was used.

They are a really annoying device. Inaccurate and way too bright for the rest of the panel. Most people just disconnect them. I took my original instrument cluster off awhile back to refurbish it and put on a replacement one that I had in the shed. The lights on it are on all the bloody time. As I can't be bothered to take this one off until I fix the other, I have an attractive piece of black tape covering them.

SaKson7-lunchboKsrider wrote: I have an attractive piece of black tape covering them.

Don't leave the black tape on for too long, some tape adhesives have a tendency to etch into the clear plastic face of the cluster


Hmm how does he know that !!

....And i would have too if you hadn't told me!

Most people do not know there are little pots for adjusting when the low fuel lights come on. I have the later set up with a single red low fuel light on my daily rider and I have the light set to come on with 3/4 of a gallon left, and it is very reliable.

Themason wrote:Most people do not know there are little pots for adjusting when the low fuel lights come on. I have the later set up with a single red low fuel light on my daily rider and I have the light set to come on with 3/4 of a gallon left, and it is very reliable.

Have you any pics of where the pots are. My K1100 comes on when there is about 7 lts left and I would like to change it.

Yes, please show us where it is...here is a picture of the level switch pcb.

Rick, as you see...it isn't any pot on the pcb.

But you can adjust the switch at the float sensor...
which I did describe in an earlier thread (~1 year?).....
which you also did reply in (and Charlie).....
about a float sensor issue.

EDIT: here.

That float sensor, Inge, how much can you "bend" it ? My problem is the sensor knocks against the side of the tank when it is full....tick, tick etc. when the bike leans to a certain point.How pliable is the sensor...don't want to break it etc..

You should be careful with the sensor itself, but the arm can be adjusted.

Grab the arm somewhere in the middle, and hold it steady while adjusting the outer end of the arm as needed.

A closer look at the year of Themasons bikes, they probably got a thermistor sensor.

On both the early (two lamp), and the later (single lamp) version the current to the
thermistor(s) self heating circuits could be adjusted (nomally set to 95 mA).

Later version:

stan you get used to the noise ...forget it mate ...else you will end up with a false indication of fuel left

mine does the same ...but i dont want to put too much leverage in it to get it away from the side and top of the tank ....its been good for 25 years ...i dont want it to break in the next couple because i played with it ..

Thanks people. Charlie, if I rev the motor more and go faster, this should be loud enough to cover the noise in the tank?
Alfa Romeos that came to Australia in the 70s and 80s had very good radios....to cover the sound of the car rusting.

This may seem like some useless pursuit, but I'm wondering if anyone has the ability, training & experience to help me with a fuel light board circuit.
Again, You can just throw an old shoe at me if I'm being ridiculous here but I'm trying to "Reverse Engineer" a fuel light system.
I have a 1985 K100rs. I used to have a newer 85K100rs as well, Although few people have any love for the original "Duel" fuel lights, mine on the 1st bike worked pretty well & I liked them.
That said, I no longer have the original instrument cluster from my current 85 K100rs. I currently have a speedo unit on it removed from a 1987 K75S. It has a 9 screw housing, Gortex vents and a single 4L fuel lamp. I also have a used 1985 k100rt speedometer assy that I'm using for various parts It had 235,000 miles on it
The object of my "ridiculous adventure" is that I'm attempting to reverse engineer the newer speedo assy to operate with both early fuel lights.
I have completed my work so far but I have yet to test it because I have another unit on the bike for an extensive test that I intend to sell. If everything operates properly on that unit.
So.....On to the story: I have the early 2 light board designed for a 7 screw housing in the newer 9 screw unit. I have both lights installed in the foil ribbon. I have fabricated and added a second "connection Pin" in the foil ribbon for the second lamp & connected it to the early board (T1).

I have changed the lenses in the front to reflect the 7L & 4L lamps. I still have some doubts about the way a couple of components are screwed down to the back side of the Tach. The old style Tach. had metal plates across the back & then the fuel board componats (I don't know what they are called) are to be screwed down on top of the metal plate. The plates do not appear to be electrically connected to anything, but the newer tach. does not have them. So the components are screwed down directly to the plastic housing.

>>>I just realized looking at the photo above that I still need to fabricate and install another pin in the foil ribbon at the other end of the fuel board, 2 pins to the left of the pot.
Anyway.....continuing, just before I closed up the housing for a test, I spied 2 more defects that I have attempted to correct but I have some considerable doubts about:
#1 All 3 legs of the Pot. (Shown above) were found to be completely broken loose from their solder connections.
#2 The Diode in the following photo had never been installed in the hole in the board on one end & of coarse never connected & soldered. See below>>>

I have re-soldered the 3 legs of the Pot. re-installed the leg of the diode & soldered it to the board as well.

I regret that I did not get some pics of the back side of the board and the solder joints.
So here are some questions: I'm not good at following those tiny printed circuit ribbons across a board under the green shellac. I'm thinking that it's entirely possible that I have some of the legs on the Pot shorted over to the adjacent circuit or across 2 circuits. The same concern exists with the one end of the diode.
I have seen the electrical schematic of the fuel lights circuit, but I'm not technical enough to interpret it.
I'm hopeful that someone has a closeup photo of the bottom of the early 2 lamp board & can help me compare it to the schematic. (A formidable task).
Finally I'm wondering what you think my chances of succeeding are, once I get the other foil ribbon pin soldered in?
PLEASE do not tell me "it's easier if you just go out and get another used 85 speedometer and fix it up"
Regards, ibj...

Inge K. wrote:A closer look at the year of Themasons bikes, they probably got a thermistor sensor.

On both the early (two lamp), and the later (single lamp) version the current to the
thermistor(s) self heating circuits could be adjusted (nomally set to 95 mA).

Later version:

I believe I may have completed this project.
Today I road tested with a newer IP cluster with a single 4L red lamp. I drove about 10 US miles past the point that the solitary Red 4L warning light had come on and stayed on.
I then mounted up my regular speedo (originally from an 87 K75s) on the 85rs.
Turned on the key, 2 seconds later the 7L light came on, 2 sec after that the 4L light came on.
I'm cautiously optimistic that I may just have pulled this off.
Since, .......I have filled the tank...... In the next few days I hope to get some miles to see how the lights react as the tank goes from full to empty.
Fingers crossed.
As a side note I wouldn't recommend attempting this mod. (who would want to anyway? LOL).
To recap: I started with a 9 screw Gortex vented, 4L red light speedo from an 87 k75s.
Instead of just changing the entire foil circuit as Inge recommended......I stumbled around......first installing an early W/L board and attempting to mill out a new area on the edge for the additional housing screw to pass by it. I made sufficient room for the screw, but got it wrong in not making enough room for the support stand that surrounds the screw. I broke the W/L board in half when trying to install the back. Another used board was obtained & I elected to omit the offending housing screw and support shoulder and go with 8 screws only, instead of trying to grind out the corner of the board. A small dab of RTV silicone was used in the vacant hole to keep weather sealing integrity. Almost together when I discovered one of the 2 potentiometers on the board had all three solder joints broken off + 1 end of 1 diode on the board had never been connected to the board from the manufacturer!......not sure why? My soldering skills & vision are questionable when working on these tiny boards, but I think I managed to get all 4 solder joints connected back to the board. I felt it doubtful that I had not crossed a circuit or possibly still had an open in the tiny foil connections. I also found that the tachometer plastic housing on the newer IP cluster was minus the 2 aluminum plates on the back. After some consideration, I decided these are for "heat sinks" for the 2 "op-amp" control devices on the W/L control board and probably required. Fortunately, I had a couple in my spare speedo junk parts.
Next I discovered that my later style model blue foil printed circuit, was lacking 2 pins in the push in pin array to connect with the 8 sockets on the early fuel board. I made 2 pins from a small cotter pin, inserted them down through the vacant holes in the foil circuit into the respective sockets and soldered them to the foil.
Last, I found that I needed a #8 pin in the main speedo connector (omitted from the later model IP Clusters.
I had a difficult time fabricating & installing that extra pin but I was able to use a long pin, cut from an old circuit foil, drill a hole in the plastic base & solder the pin to the foil....afterwards, the connection to the foil was found to be incomplete so a small jumper wire had to be soldered from the pin to the foil. Last a small gob of epoxy was added around the base of the #8 pin for added support and the rubber pin gasket was re-installed...... Upon test fitting the back housing cover, the lump of support epoxy around the #8 pin was found to obstruct the cover from sitting completely down flush with the housing. A small depression was ground into the inside of the back cover with a dermal to provide the needed clearance. The 2 red lenses in the speedo face were exchanged for an original yellow 7L lens and a red 4L lens. (Unfortunately I installed them in the wrong windows, so I had to go back in to the front of the speedo another time to switch their positions).
The tank was filled with fuel and road tested with a known good IP cluster until the fuel level illuminated the lone 4L light on that unit. Ten more miles were driven to make sure the fuel was just below the 4L trigger point.
The modified 9 screw unit (minus the 1 screw) was installed on the machine with the approx. known sub-4L fuel level.
Turning on the key all fuel lights were off as the sensors had time to heat up..... 2 seconds later the yellow 7L light came on followed by the red 4L light 2 seconds after the first one. Yipppppeeeeee!.
Next the tank was refilled and the trip Odo. reset to zero.
I expect to road test about 175 miles in the next few days to observe if the fuel lights will function as designed. (some would describe that as "poorly"....LOL)
I will report the final outcome in a few days.
....I'll never attempt that one again!
regards, ibj....