1987 K100 fuel warning light

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Quzzy
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1987 K100 fuel warning light

Postby Quzzy » Sun Oct 28, 2018 11:35 am

Hi all
Fuel tank with float type sender.
Single bulb warning light (bulb OK)
Originally with fuel gauge, now removed.

The bulb fails to illuminate when the tank is empty, flat and arm intact and moves freely.
4 way "oval" plug from tank clean and tight. brown,yellow,green and white.

Just to test the circuit if I supply direct live to the outgoing side of the plug, should the bulb light?
I cant find a decent wiring diagram that shows the colours I have going to this plug.
Thanks in advance
1987 K100
2002 RT1150

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Galactic Greyhound
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Re: 1987 K100 fuel warning light

Postby Galactic Greyhound » Sun Oct 28, 2018 6:34 pm

Hi Quzzy,

I have had a look at a K100 RS/RT/LT 1985-on wiring diagram:

The 'Low Fuel' light has one side connected via a Green/Black wire to +12v via the Instrument Panel connector pin #6 and Fuse #1.
The other side of the light is connected via a Black wire to a 'Low Fuel' electronic module whose function I believe is to dampen the input signals from the 'Low Fuel' switch so that the Low Fuel light only lights when the Low Fuel signal is ON for a fixed time e.g. 10 seconds.
This is to stop the Low Fuel light flashing On/Off as the fuel level approaches 'Low'.

The 'Low Fuel' signal is sent from the Fuel Level Sender to the Low Fuel Damping module on the White wire via pin #7 on the Instrument Panel connector.
The setup appears to be similar to that used on the R1100RT whereby the Low Fuel switch sends an earth to the Low Fuel Damping module input (White wire) and the module then sends an earth to the Low Fuel light after the damping period has passed (say 10 seconds) as long as the Low Fuel signal earth is still present on the input.
This causes the Low Fuel light to illuminate.

When the fuel level is restored above the 'Low' level, the Low Fuel switch goes Off so removing the earth from the Low Fuel Damping module input (White wire) and the module then removes the earth to the Low Fuel Light again after the damping period has passed (say 10 seconds) so causing the Low Fuel Light to go Off.

The Fuel Level Sender Unit Yellow wire is for additional Instruments (Fuel Gauge?).
The Fuel Level Sender Unit Green/White wire is the +12v to the Fuel Pump via Fuse #6.
The Fuel Level Sender Unit Brown wire is a common earth.

Summary.

With the Ignition ON:

1. You need to check that there is +12v from Fuse #1 appearing on the Instrument Cluster pin #6 Green/Black wire from Fuse #1.
Quick Check: If your Choke light is working then this +12v is present on the Instrument Cluster.

2. Apply an earth on the White wire from the Fuel Level Sender to the Instrument Panel connector pin #7 and HOLD this earth on for at least a minute to allow the Fuel Level Damping Module to operate.
When the module operates after a period it will send an earth to the Low Fuel light to illuminate it.

3. The Fuel Level Damping Module is supplied with power from the Instrument Panel power via Fuse #1 and common earth.

4. Check that when the Float Arm is in the lowest position (no fuel), that an earth is present on the White wire coming from the Low Fuel Switch (i.e. Check the continuity from the Brown earth wire to the White signal wire).
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
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Re: 1987 K100 fuel warning light

Postby Quzzy » Sun Oct 28, 2018 9:32 pm

CED as always you make owning a BM affordable and "understandable"
I have the choke light so tomorrow (its 9:30 pm here and close to snowing!) I will do the earth test, thanks

BTW the RT oil leak remains unresolved and is provisionally sold for 500 euros to rid me of the problem.
The R60/5 has been swapped for the bobbed K I am referring to above that I built for a friend, plus cash that enabled this to join the familyImage
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1987 K100
2002 RT1150

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Galactic Greyhound
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Re: 1987 K100 fuel warning light

Postby Galactic Greyhound » Sun Oct 28, 2018 10:30 pm

Ah - a Simca! :grin:

Does it have the Simca flat engine?

It's 0C here at the moment (2130 hrs) with clear sky and I can see Mars!
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!

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Re: 1987 K100 fuel warning light

Postby Mjolinor » Sun Oct 28, 2018 10:58 pm


It's 0C here at the moment (2130 hrs) with clear sky and I can see Mars!
Then eat it or someone else will.

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Re: 1987 K100 fuel warning light

Postby Quzzy » Mon Oct 29, 2018 12:31 am

1300 inline 4 upfront, conventional layout RWD....prefer Snickers anyway ;o)
1987 K100
2002 RT1150

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Re: 1987 K100 fuel warning light

Postby Quzzy » Mon Oct 29, 2018 10:01 am

Soooo.....
No earth to white wire from tank (empty)
No light when pin 7 earthed, however should I be doing this with the plug in place because the positive side is not energised (choke light doesn't come on)? Should I be probing into the back of the plug while connected? Difficult?

But if there's no earth from the white wire out of the tank, then the sender needs cleaning/replacing?
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Re: 1987 K100 fuel warning light

Postby Galactic Greyhound » Mon Oct 29, 2018 11:04 am

Soooo.....
No earth to white wire from tank (empty)

The Float Arm is likely connected to a PCB track. At the end of the track (low fuel) the Float Arm wiper contacts an earth-connected section which sends the earth to the white wire - you need to get this on a bench and check the continuity between the earth coming in and the white wire going out.

You do have an earth connected to it if you were looking for an earth?

Otherwise check continuity from where the earth goes in to the white wire going out.


No light when pin 7 earthed, however should I be doing this with the plug in place because the positive side is not energised (choke light doesn't come on)?

Yes - the Instrument Cluster connector should be connected so as to pass the earth through to the Low Fuel Damper Unit in the cluster.

The Choke light should come ON when the Choke is operated which indicates that power is going to the Instrument Cluster and Damper Unit from Fuse #1 - if it is not coming on then the Low Fuel light can't work along with some other dash lights.

Remember that the Damper Unit is really a Timer so the earth needs to be present on the input side for a period of time CONTINUOUSLY before the Damper Unit sends an earth to the Low Fuel Light.


Should I be probing into the back of the plug while connected? Difficult?

Just send an earth on the White wire from the 4-pin Fuel Sender connector.
If that doesn't work you need to move the earth to the Instrument Display connector pin 7, then if still nothing to the Damper Unit input then to the Low Fuel light.


But if there's no earth from the white wire out of the tank, then the sender needs cleaning/replacing?

Have you got an earth connected to the Sender Unit in the tank? It won't be there if you have disconnected the Sender Unit connector.

Either jumper an earth into the Sender Unit or check for continuity from the earth pin on the Sender connector to the White wire (Sender side) on the Sender connector with the Float Arm in the Low Fuel position.

It is odd that you have TWO faults - check that there is actually an earth present if you are chasing an earth and that the Ignition is ON when checking the Low Fuel light.
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
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Re: 1987 K100 fuel warning light

Postby Quzzy » Mon Oct 29, 2018 11:18 am

Just now jumped an earth to the plug white and after a few seconds the light lit. So all is well after the plug

Great - the Instrument Cluster part is working! :grin:

Using my meter on volts, red to positive battery and black to white pin on tank side, shows no earth, ie zero volts, so must be the sensor? I guess I need to get a new seal before I disable the bike by removing it?

Not necessarily - the earth you are looking for with the Voltmeter comes from the bike frame common earth point to the 4-pin Sender connector BIKE side Brown wire.

If you have the Sender connector DISCONNECTED then the earth cannot get to the TANK side Brown wire so you need to jumper both sides of the 4-wire connector BROWN wires to each other.

If that doesn't work, check that there is indeed an earth coming from the bike frame on the Sender connector BIKE side Brown wire.
1987 K100
2002 RT1150

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Re: 1987 K100 fuel warning light

Postby Quzzy » Mon Oct 29, 2018 4:08 pm

This afternoon I basically did this
http://www.k100-forum.com/t9265-messing ... uel-sender
The ohms measured correctly and the unit is in clean condition (i know the ohms are not relevant to me as Im not using a gauge but no harm to check ;o)
So rheostat cleaned and the two panel section that controls the light. contact arms tweaked to be sure of good contact.....and.....no change
The brown is earthed either side of the plug.
In the week I will take the unit out again and test it in the plug on the bike....somehow the sweeper arm is not making an earth contact, but buggered if I can see where the failure is!
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Re: 1987 K100 fuel warning light

Postby Galactic Greyhound » Mon Oct 29, 2018 5:35 pm

Hi Quzzy,

That is a good link you found and will be useful to you.

OK - if I understand correctly, you have the bike frame earth coming into the 4-pin Sender connector (bike half) and the earth is leaving the connector (Tank half) and going to the Sender unit board with the wire winding and Low Fuel contact.

There is therefore a break in the earth connection between the Sender connector Tank half (Brown wire) and the Sender connector Tank half White wire when the Float Arm is in the 'Low Fuel' position.

This earth goes via the Low Fuel switch part of the Sender as you have found out.

To test this to find out exactly where the break is occurring carry out the following:

1. Remove the Sender Unit onto a workbench with a good light.

2. Set your Multimeter to measure Resistance and choose a low resistance range say 400 Ohms or nearest.

3. Touch your meter leads together - the meter should read zero Ohms (this proves the meter is working OK on the Resistance setting - ALWAYS do this first before doing any Resistance/Continuity tests).

4. Connect one meter lead to the 4-pin connector Tank half Brown wire.

5. The other meter lead is your probe - touch this to the SAME Brown wire where the other lead is connected and the meter should read zero Ohms.

6. Now follow the Brown wire to where it is connected to the Sender board with the wire winding/ Low Fuel Switch contact - touch your probe to this connection - the meter should zero Ohms if you have continuity to that point.

7. Now examine the Sender board with a magnifying glass to see how the Brown wire gets connected to the Low Fuel Switch part of the board.

8. Probe this connection point and you should read zero Ohms proving continuity to that point.

9. Now move the Float Arm to the Low Fuel position while observing how the wiper makes contact with the Brown wire connection point of the switch.

10. Probe the wiper as it makes contact with the Brown wire contact point - you should read zero Ohms if the wiper is making good contact with the Brown wire switch contact.

11. Observe how the White wire is connected to the wiper part of the switch - probe the White wire connection - the meter should read zero Ohms indicating continuity through the wiper.

12. Probe the White wire pin on the 4-wire connector half (Tank side) and the meter should read zero Ohms indicating continuity to that point.

13. Keeping the probe on the White wire pin, move the Float Arm off the Low Fuel position and the meter should read 'infinity' Ohms indicating no continuity.

NOTE: The Brown and White wires may be reversed on the switch with the Brown wire going to the wiper and the White wire going to the fixed contact - it doesn't matter, you are only checking to see if there is continuity through the switch when the Float Arm is in the Low Fuel position.
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!

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Re: 1987 K100 fuel warning light

Postby Quzzy » Mon Oct 29, 2018 6:00 pm

Excellent description, thanks
1987 K100
2002 RT1150

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Re: 1987 K100 fuel warning light

Postby Galactic Greyhound » Mon Oct 29, 2018 8:29 pm

Hi Quzzy,

Looking at the photos in the link, it would appear that the cable from the Sender 4-wire connector goes to a plate on the tank which seems to use a sealing O-ring.

This is similar to my R1100RT Fuel Pump Plate arrangement.

If so, the 4-wires on the Sender connector will go to a sealed electrical Pass-Through connection on the plate - the wires will likely change colour on the other side of the Pass-Through pins where they go to the Sender Float Arm Unit.

Be aware that I have had problems with these Pass-Throughs whereby they go high-resistance from one side to the other.
I don't know why this should be but it affected the Fuel Gauge reading on my R1100RT until the Pass-Through connection for the Gauge eventually failed completely and I had to get a new Fuel Plate.
The Pass-Through pins seem to be prone to this fault.

This could mean that the Brown frame earth on the Sender 4-wire connector (Tank half) will go to the tank plate outer Pass-Through pin connection but may be open circuit WITHIN the Pass-Through itself so that the earth is not even getting as far as the Sender Float Arm Unit.

Therefore, when you get the Sender Unit removed from the tank, check that there is continuity from the Brown wire pin on the Sender 4-wire connector (Tank half) to the INTERNAL side of the Pass-Through pin as this may be where your break is.

The outer Pass-Through pins on my R1100RT are covered with a cap which appears to be glued on and I did not try to remove but the pins on the inner side are fully exposed and you will be able to test them from this side to your 4-wire Sender connector (Tank half).

LATER EDIT: Maybe not the problem, as the Brown earth wire also supplies the Fuel Pump earth so any problem here would affect the pump - worth checking out anyway though! :smile:
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!

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Re: 1987 K100 fuel warning light

Postby Quzzy » Mon Oct 29, 2018 8:44 pm

you are correct, they turn into dark green. I will include this check in the week, thanks again
1987 K100
2002 RT1150

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Re: 1987 K100 fuel warning light

Postby Quzzy » Tue Oct 30, 2018 1:14 pm

On previous attempts I left the wires to the fuel pump attached and worked on the sender next to the tank.
Thought I would have a bash at removing it properly this lunch time so I can "bench" test it on the bike.....is there a secret to undoing the 7mm nuts on the pump? The pump turns when I finally get a socket or ring spanner on and obviously theres not room to get another hand in through the filler hole
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Re: 1987 K100 fuel warning light

Postby Mike D » Tue Oct 30, 2018 1:59 pm

There are two prongs in the pump holder. Press these inwards to release the pump. There will be then enough slack on the cables to get the pump near the petrol cap mouth, where you can then use two hands.

Mike

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Re: 1987 K100 fuel warning light

Postby Quzzy » Wed Oct 31, 2018 7:31 am

Thanks, I nearly did that but was afraid to disturb something else...
1987 K100
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Re: 1987 K100 fuel warning light

Postby Quzzy » Wed Oct 31, 2018 1:11 pm

Its out...and it all works!
It appears that the arm has previously been bent and not deflecting fully.
Thanks guys
1987 K100
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Re: 1987 K100 fuel warning light

Postby Quzzy » Wed Oct 31, 2018 1:12 pm

Oh and for reference one of the fuel pump nuts is 7mm, the other 8mm
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Re: 1987 K100 fuel warning light

Postby Mike D » Wed Oct 31, 2018 2:05 pm

Oh and for reference one of the fuel pump nuts is 7mm, the other 8mm
That's how the OEM pump was, so that you couldn't fit the wiring bac on incorrectly. A number of aftermarket pumps have the same diameter terminal.

Mike

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Galactic Greyhound
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Re: 1987 K100 fuel warning light

Postby Galactic Greyhound » Wed Oct 31, 2018 2:29 pm

Great news Quzzy - well done on finding the problem! :grin:
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!


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