Instrument cluster and low fuel light

[motodude]

A while back I noticed the low fuel light was not lighting up on my K75 (no gauge--just a light).  So, I thinking the bulb was the most likely culprit, and cheap, I replaced it.  No joy.

At this point I've done the following:

1) Double-checked the bulb, it lights up.  Tested w/ bulb in black plastic holder from cluster.
2) Checked the continuity between the connector at the tank (white wire) and the connector at the instrument cluster (pin 7).  Good continuity.
2) Replaced the sending  unit (I know, I know).
3) Swapped the instrument cluster off my K100.  Hit the key and the low fuel light lights up.  (Shoulda done this first.)
4) Pulled the instrument cluster apart.  Put power to pin 6 (switched power) and grounded pin 7 (out to sending unit), still no light.

Am I correct in assuming that the sending unit varies the resistance to ground?  Or, is this some sorta dueling power sources like the charge light?

One electrical diagram I have shows pin 8 coming from the sending unit too.  But, the pin-out diagram for the cluster shows pin 8 as an ABS line (which I don't have).  I'm not sure if this is significant or not, but I've been ignoring pin 8 for now.

Are there any relatively common failure modes for this behavior that I have missed?  I know the connector between the tank and the bike/cluster is a common failure point but using the other cluster, the low fuel lit up, so I'm assuming the connector is good (also, the bike runs so I know the pump is getting power).

Any ideas?

Thanks,
Tom

[Scott_]

I suppose it's possible you have a bad diode internal to inst cluster.
When you have it connected, do you read any voltage on pin 7 when it's UNGrounded? Or the white wire at the tank connector.
I think you are on the right track that the power is supplied to the lamp internal to the inst cluster then out on pin 7 to be grounded in the sending unit when it reaches the point of low level switch contact. It should be just a straight switch, not variable.

[motodude]

I'm assuming variable as I believe it is the same sending unit used for gauges too.

I hooked up the cluster to a jumper, pos to pin 6 (switched power) and attached a dvm between pin 7 (to sending unit) and ground.  I got ~12.5v.
Then, I plugged the cluster into the bike, connected a dvm between ground and the white wire on the connector to the tank and turned on the key, I got ~10.5 volts.

In both cases the light did not light up.

I understand continuity and basic electrics.  I don't know much about about diodes except that they only allow continuity one direction.  What this is telling me is that there is another path through the cluster that does not include the bulb.  Something is shorted?

Thanks,
Tom

[Inge K.]

I'm assuming variable as I believe it is the same sending unit used for gauges too.

The level sensor has to separate circuits, one for the lamp (switch), white wire.
And for the gauge it`s a variable resistor (yellow wire).

The lamp has its own pcb inside the cluster (top left corner, wiewed from behind) check its connectors.

Inge K.

[Rick G]

The same unit is used for gauges but the sender has two very distinct parts.  One is a wire wound resistor with a wiper to contact the wire depending on the fuel level the other is a wiper which runs across a plastis part and then at low fuel level contacts the metal part and so brings the light on and that is what yours uses.  If the light works with the K100 unit then the fault is either the unit or the multi pin plug. As Scott suggests the diod or check the plastic printed circuit parts for contact areas either cracked or folded back and not contacting at the bulb plug.

[motodude]

If the light works with the K100 unit then the fault is either the unit or the multi pin plug.

As Scott suggests the diod or check the plastic printed circuit parts for contact areas either cracked or folded back and not contacting at the bulb plug.

Understand the part about the sending unit providing two controls.

I don't understand your statement about the light working with the other cluster and the fault potentially being with the multi-plug?  Doesn't the fact that the light comes on with the other cluster prove that the problem is in the cluster?  What am I missing?

I went back out and carefully inspected the the pcb's and the traces on the blue foil thing.  I don't see any issues.  The transitions from the blue foil to the bulb contacts appear solid.

Thanks for your help!
Tom

[Rick G]

The multi pin plugs do give problems and seeing as the light works with the K100 instrument panel it could be that the plug won't work because of different pins (round or square) and the plug or pins needs a tweak to work.  I tend to forget sometimes that many people dont know as much about the changes over the years and make these assumptions, sorry.

[Inge K.]

First check that the earlier mentioned pcb receives positive and ground.
Ground the signal input, after a short time delay you should measure ground at the output (to the lamp).
If not the pcb is your problem.

Inge K.

[motodude]

The multi pin plugs do give problems and seeing as the light works with the K100 instrument panel it could be that the plug won't work because of different pins (round or square) and the plug or pins needs a tweak to work.  I tend to forget sometimes that many people dont know as much about the changes over the years and make these assumptions, sorry.

Gotcha.  I was thinking you were talking about the multi-pin plug at the tank (in-line, right side of bike), not the multi-pin plug at the cluster.

They do differ in that the screw that secures the connector uses the "top" hole on the K75 and the "bottom" hole on the K100, so there could be differences there.  The '87 K100 does not have the original cluster.

Thanks,
Tom

[motodude]

First check that the earlier mentioned pcb receives positive and ground.
Ground the signal input, after a short time delay you should measure ground at the output (to the lamp).
If not the pcb is your problem.

Inge K.

Thanks Inge.  My multi-meter took a dump last night.  Usually, if I turn it off for a while it will come back.  I (think I) figured out which connection is which and performed the test you indicated.  plugging in the cluster to the multi-plug, turning on the ignition and grounding the control connection produces slightly over 51M-ohms between the control out and ground .  I also verified that power is getting to the bulb.  Looks like it is the pc board.

Question, what is the board's purpose?  It apparently acts as a relay for the bulb w/ maybe a time delay?  If so, would it be possible to just bypass the pcb and use the switch in the tank directly?  Or, will that create a fireball?   :yow   

I also got this feedback from PaloAlto Speedo, "I am sorry but the parts that we need to repair this particular problem are no longer available to us. MotoMeter Germany has discontinued all of these parts. We have certain K-Bike repair parts left, but not the low fuel circuits. We repair quite a few K-Bike odometers, clocks, gear indicators, lighting, but not your issue. Sorry that we are not able to help you."

So, I'm guessing a used replacement is is my only option at this point.

Thanks again for your help,
Tom

[Inge K.]

The pcb just delay and memorises the signal, so you don`t get a annoying on,off,on,off warning.
No problem to bypass it, untill you find another one.

To be on the safer side you could change the bulb to a LED, as it draws less current.
I`ll guess the pcb passing less current than the bulb to the level sensor......earlier mentioned fireball :yow

(Don`t blame me when you smashing the cluster because of this annoying light, when riding after dark)

Inge K.

[motodude]

The pcb just delay and memorises the signal, so you don`t get a annoying on,off,on,off warning.
No problem to bypass it, untill you find another one.

To be on the safer side you could change the bulb to a LED, as it draws less current.
I`ll guess the pcb passing less current than the bulb to the level sensor......earlier mentioned fireball :yow

(Don`t blame me when you smashing the cluster because of this annoying light, when riding after dark)

Inge K.

No worries about blaming you for the flashing light. Those 2v clusters are made outa pure unobtanium, I doubt I'll be smashing any.

I don't know much about this [electronic] stuff, but I would think it would not be too difficult to come up with some sort of a delay circuit, very similar to the pcb board.

 Frankenduck's LED kit has kinda been on my list anyway.

Thanks again,
Tom

[frankenduck]

I've never really played with the low fuel light pcb on clusters but I've got some parts clusters hanging around and may be able to help out next week when I get home.

[motodude]

I've never really played with the low fuel light pcb on clusters but I've got some parts clusters hanging around and may be able to help out next week when I get home.

I put the cluster back together tonight.  I'm going to work on the rack for a while, so waiting a week or so is no big deal.

I'd need to figure out how to RnR the pc board w/o damaging the blue foil conductor thingy.   :dunno  Not sure what its supposed to be called.  I'm not sure if it can be (or I can) solder it w/o destroying it.  Maybe easier to just bypass the foil thing with some wires. 

Thanks for offering to help out.

Tom

[Rick G]

A small 12v relay with a large capacitor across it would be a good slow down for the light. I will do a bit of messing around and experiment to see how it would go. You would not entirely elimate the on-off light but stop most of it.

[DRxBMW]

I also got this feedback from PaloAlto Speedo, "I am sorry but the parts that we need to repair this particular problem are no longer available to us. MotoMeter Germany has discontinued all of these parts. We have certain K-Bike repair parts left, but not the low fuel circuits. We repair quite a few K-Bike odometers, clocks, gear indicators, lighting, but not your issue. Sorry that we are not able to help you."

So, I'm guessing a used replacement is is my only option at this point.
Thanks again for your help,
Tom

Tom,
Contact these folks at the link below, they may be able to help.

http://www.instrumentclusters.com/

I have a K 100 broken pod somewhere in the basement.  dunno know if the crb is any good though.

[motodude]

Tom,
Contact these folks at the link below, they may be able to help.

http://www.instrumentclusters.com/

Thanks Bob.  I have sent them a request for a quote via their web site.  Hopefully, the response is positive.

Tom

[DRxBMW]

Tom,
Contact these folks at the link below, they may be able to help.

http://www.instrumentclusters.com/

Thanks Bob.  I have sent them a request for a quote via their web site.  Hopefully, the response is positive.

Tom

It's GARY NOT Bob 

KBMW list reported excellent work done by  Instruments.com. 

Good Luck

Off too the LineX dealer for a spray job on my GS bumper scuff guards.

[johnny]

greetings bob...

that linex comes in custom colors... i would get pennsylvania clay red...

j o

[motodude]

Tom,
Contact these folks at the link below, they may be able to help.

http://www.instrumentclusters.com/

Thanks Bob.  I have sent them a request for a quote via their web site.  Hopefully, the response is positive.

Tom

It's GARY NOT Bob 

KBMW list reported excellent work done by  Instruments.com. 

Good Luck

Off too the LineX dealer for a spray job on my GS bumper scuff guards.

Oh Jeebus!  My apologies Gary.  Trying to do too many things at once (again).