Author Topic: 1985 K100 RT Instrument Cluster Removal  (Read 16983 times)

Offline rogan

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1985 K100 RT Instrument Cluster Removal
« on: May 26, 2015, 01:59:17 PM »
Newbie here, I have a 1985 K100 RS with a full RT fairing. I have several instrument cluster warning lights out and would like to test/replace them.  Looking at the Clymers manual and the bike, it appears that I will have to remove most if not all of the fairing to get at the back of the instrument cluster to remove it.  Just removing the windshield doesn't appear to provide enough access, and the windshield screws have backing nuts that are not readily accessible anyway without digging into the fairing  Is this correct?  I have looked at some of the topics here related to K75 fairing removal, and K100 instrument cluster removal, but it seems mine will be more involved. Any sage advice? 

Thanks.

Rogan
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  • 1985 K100RS

Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #1 on: May 26, 2015, 03:55:09 PM »
OK, the good news is that I was able to get at the back of the instrument cluster after removing the lower leg shield and storage pockets. 

Couple of pieces of bad news though.  A previous owner seems to have replaced a missing (I'm guessing)backing plate in the lower center of the back of the housing with a thin piece of wood with epoxy dribbled on it, and screwed it into the housing, so it covers most of the opening, but certainly isn't dust or watertight.

Also the only bulb that actually seems to be burned out is a green coated general illumination bulb in one corner.  The oil pressure light and the low fuel lights that I believe are supposed to light when the ignition key is first turned to the on position before starting test good, but do not work on the bike.  I'll search for other threads, but I assume this means a bad connection, sensor, or other component somewhere else in those circuits.  Any tips here would be appreciated.

Thanks.
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Offline billday

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #2 on: May 26, 2015, 09:48:00 PM »
The low fuel lights do not "test" when you turn on the key.

As for the bad bulb: The bulb gets wedged into a square opening, and on either side of the opening is a flap of sheet-like copper conductive material. Make sure that flap is draped over the opening so it can make contact with the bulb holder. Lots of times it gets folded underneath its self.
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Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #3 on: May 27, 2015, 01:10:37 AM »
My rider's manual says on p. 12 that the oil pressure, battery charge, choke, rear light monitor, neutral, and 5 liter fuel warning/telltale lights are supposed to come on when the ignition switch is in position 2 before starting.  My bike has two fuel warning lamps, for 7 liters and 4 liters, neither of which have come on with the ignition switch. So you have this two fuel lamp setup, and the two lights do come on in sequence as the fuel drops, even though they don't light up before starting?  That would be great (I haven't run the fuel down yet).

How about the coolant temp light? Page 12 doesn't say it should come on with the ignition switch, but page 34 says to check that the coolant temp warning light is operating correctly, so I was thinking that might come on before starting also. If not, any idea what the procedure would be for checking it?

Perhaps the only one that isn't working is the oil pressure light circuit.

All the brass contact flaps on the circuit board look good.

Thanks again.
  • Minnesota
  • 1985 K100RS

Offline rbm

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #4 on: May 27, 2015, 07:12:46 AM »
How about the coolant temp light? Page 12 doesn't say it should come on with the ignition switch, but page 34 says to check that the coolant temp warning light is operating correctly, so I was thinking that might come on before starting also. If not, any idea what the procedure would be for checking it?
Since you have the cluster off, take the bulb out and test it with a 12V battery.  That will confirm the bulb as being good or bad. If you want to test the circuit that activates the bulb, ground Pin #A3 on the temperature relay in the relay box under the tank (after first removing the relay from its socket).  That should illuminate the bulb on the dash.

Quote
Perhaps the only one that isn't working is the oil pressure light circuit.

All the brass contact flaps on the circuit board look good.

Thanks again.
The oil pressure light should come on with the key in position 2 because there will be no oil pressure in a motorcycle that is turned off.  Once the motor starts and the oil pressure builds up, the light should extinguish.  If yours is not coming on with the ignition, there is a problem with either the bulb or the oil pressure sensor, located in the water/oil pump.
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #5 on: May 27, 2015, 11:05:09 AM »
Rbm, yes, I checked all the warning bulbs after removing them already and they were good, unfortunately. Thanks for the next steps for the coolant and oil pressure circuits.
  • Minnesota
  • 1985 K100RS

Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #6 on: June 09, 2015, 02:37:47 AM »
Rbm, I tested the coolant temperature circuit as you suggested, and the dash light lit up, so that should be OK.  I planned to replace the oil pressure sending unit, since cleaning the contacts made no difference.  Before removing the sender I wanted to clean the crud from the area, and in doing so, I found one crack in the insulation on the wire coming from the sender near where it enters the engine.  I reconnected the wire and tried again, and this time I did get the light to come on with the ignition switch on, so hopefully it will keep working.

The remaining warning lights that aren't working are the 7L and 4L low fuel lights.  I've run it nearly to empty and neither lit up.  I may end up relying on the tripmeter once I get a better idea of the gas mileage. It looks like I need to remove the gas tank to be able to access the wires and connections that run along the frame from the fuel sensor.  Any suggestions that anyone may have about other tests to run on the sensor or its circuit would be appreciated.  I understand that there is a separate printed circuit board inside the cluster for the fuel lamps, but I wasn't able to see any physical flaws when I had the cluster apart before.

Thanks again.
  • Minnesota
  • 1985 K100RS

Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #7 on: June 16, 2015, 03:23:55 PM »
I'm back looking at my problem with no low fuel light warning lights. One question I have is about the pin connectors on the back of the instrument cluster.  I'm assuming for now that the cluster is the original for my 1985 K100RS.  Is there a simple diagram of the connector pins on the cluster and which circuits they are on?  I have a schematic in the Clymers manual, but don't understand it well enough to translate it to the pin positions. For example, when someone here refers to pin 7 or pin 6, which of the two connector banks on the instrument cluster is meant, and is pin 1 at the top or bottom of the plug?

Also, each connector bank on the cluster has 11 pins, 4 at the bottom, then a gap, and 7 more up to the top.  However, the bank on the left as seen with the cluster removed and looking at its back has a small hole in the plastic base as if there may have been another pin there that broke off at one time. The wire plug-in connector for that side has 12 open slots, while the one on the right side has a plastic plug in the slot fifth from the bottom, indicating that the right side plug never had a 12th pin, but the left side may have. The wire going into the back of the socket correlating to the "missing" pin is brown/black, which is the color of one of the 4 wires coming out of the undertank connectors wired to the fuel sender after it exits the tank.

Can anyone provide some information on these questions?  I've tried to attach a photo of the pins, but it may be difficult to see the difference in the "missing" pin on the left side.

Thanks much.



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  • 1985 K100RS

Offline rbm

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #8 on: June 16, 2015, 10:16:16 PM »
This is the pinout on the back of the instrument cluster


Your blank pins correspond to pins 8 and 20.  Since 8 is missing, the cluster is probably not one made for the pre-85 with the earlier fuel level sender and therefore is probably not the original gauge cluster for your bike.  The gauge will not be equipped with the circuit needed to make the sender function nor equipped with the yellow 7L fuel level indicator.  The  gauge will have the 4L indicator but it will not function with your fuel sender.
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #9 on: June 17, 2015, 03:17:25 AM »
Rbm, thanks once again for your knowledge, and the plug pin arrangement list.  Exactly what I was looking for.  It's quite possible this is not the original cluster and is incompatible with the sender, though it does have both the 7L and 4L labels on the face of the warning lights. I suppose any of the various fuel warning components could have been replaced at some point with incompatible parts, or that the #8 pin was indeed broken off at some point.

Thanks once again for your help.
  • Minnesota
  • 1985 K100RS

Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #10 on: June 19, 2015, 09:29:33 PM »
Still looking at the instrument cluster innards to see if there is anything to explain the lack of low fuel warning lights, beyond what we have already discussed.  I opened up the cluster housing again, and noticed that there is a copper circular contact in the upper left hand corner of the blue plastic film (as you are looking at it from the back) that is not attached to another component.  There is also a circuit board in this upper left corner. I read elsewhere that this board is part of the fuel warning system though I don't know if that is correct.

Most of the copper contacts on the blue film seem to be attached through the plastic to the underside of the board with what looks to me like a rivet, or tiny spot weld.  This particular contact isn't attached to anything, though there is some kind of component underneath.  I've attached a grainy photo to illustrate. The contact at the top of the photo is unattached, the one below it has one of the "rivets" connecting it to another part.

Does anyone know if this contact should be electrically connected to the component under the board, like the one just below it is?  Is this in fact part of the fuel warning system?

Thanks for any help.
  • Minnesota
  • 1985 K100RS

Offline Inge K.

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #11 on: June 21, 2015, 04:45:44 AM »
You have the correct fuel level warning PCB (also the speedo and tacho) for your model.
But the center plastic part with the blue conductive film is from a -86 or later.
But still the 4L warning lamp should function, tho.
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Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #12 on: June 22, 2015, 01:37:51 PM »
That's very interesting.  I would have thought that it would be difficult to change out the blue plastic film printed circuits and all its connections.

I used a piece of solid copper wire and soldered it to the copper contact on the blue film where the #8 pin should be, to see if that would make a difference on the 7L warning light, before I got Inge's last message.  May not have gotten a great joint because I didn't want to melt the plastic film, but in any case the 7L light didn't light up after I plugged in the multipin connectors.  I suppose if the blue film is from the '86 and later bikes that didn't have the 7L circuit, then it wouldn't work anyway.

I guess one of the questions now is whether the blue film I have supports only the 5L warning light, and whether I have an original sending unit in the tank that is not compatible with the 5L setup, or is defective.

Thanks Inge.
  • Minnesota
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Offline Inge K.

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #13 on: June 22, 2015, 04:56:56 PM »
I would have thought that it would be difficult to change out the blue plastic film printed circuits and all its connections.
The white plastic part with bulb holders, blue conductive film and connecting pins is one part.
The later version missing the three connecting pins for the 7L warning lamp.

I used a piece of solid copper wire and soldered it to the copper contact on the blue film where the #8 pin should be, , but in any case the 7L light didn't light up after I plugged in the multipin connectors.
You also need to connect the input and output contacts at the pcb to make the circuit complete.
But the 7L warning lamp is useless anyway....starts to flash above half tank.

I guess one of the questions now is whether the blue film I have supports only the 5L warning light, and whether I have an original sending unit in the tank that is not compatible with the 5L setup, or is defective.
If you have the connector for the sender and pump in the left front corner on the underside of the tank
it's compatible with the pcb inside the instrument......the later tank have also different mountings.
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Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #14 on: June 22, 2015, 07:14:29 PM »
Ok, I'll stop obsessing about the 7L light.  Thanks for the additional insights, Inge. Would be nice to have the 4L light though.

[/quote]
If you have the connector for the sender and pump in the left front corner on the underside of the tank
it's compatible with the pcb inside the instrument......the later tank have also different mountings.
[/quote]

The connector is in the left front corner under the tank. Four wires exit the tank, go through two connectors of two wires each, and then recombine into a bundle that goes forward toward the cluster.  The wires coming out of the tank are: green/red and yellow/ green, which go into a black connector, and emerge as green/yellow and brown/white going forward; and black/white and tan(?), which go into the other connector and emerge as brown and brown/black going forward. I'm not sure if this was the stock setup or if it indicates something about which sender is in the tank.

Thanks.
  • Minnesota
  • 1985 K100RS

Offline rbm

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #15 on: June 22, 2015, 07:37:31 PM »
Sounds like the fuel sending circuit has been modified. There should be a single round white 4-pin connector to hook up to the tank as in the photo below, not two 2-pin: 


The OEM wire colouring emerging from the tank should be:

Brown/Black  (T1): 7L thermistor

Brown/White  (T2): 4L thermistor

Green/White (15):  Fuel pump power +12V

Brown  (31):  Ground

Designations in brackets are the ISO pin numbering.

It could be the thermistors in the sending unit are not functioning, causing the lights not to work.  They should read 600 ohms between ground (probably your black/white) and each individual thermistor (probably your yellow/green and tan). I'm guessing here since the harness wiring is odd as well.
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #16 on: June 23, 2015, 12:17:14 PM »
Rbm, thanks. Yes, I definitely have some ad hoc wiring.  I unwrapped the electrical tape around the wires between the tank and the black connectors.  In doing so, the connection to the four prong plug that exits the tank came apart, revealing four separate black slide-on connectors, kind of like a crimp-on connector, but not crimped. Connections weren't very clean, and evidently were held in place only by the tape wrap. The fuel pump has been working, so at least some of the connections were good. At this point I removed the tank, since I could see floating debris in the gas, and I wanted to clean it out and replace the fuel filter anyway.

I removed the large nut holding the sensor onto the tank, and pulled out a plastic covered cylinder, which I assume is the sensor, but it doesn't have a float like the others I've seen.  Maybe this is the original version that was changed on later models? Two wires enter the unit from the tank, one purple, one gray, which must come from the fuel pump.  There is an opening toward the bottom of the cylinder where you can see what wires enter the four prong plug. There are five wires: two gray, one purple, one reddish orange, and one dark brown.  The two gray wires look like they join to one of the four prongs.  I've attached some pictures, to give a general idea of the layout. Perhaps I could try to run the test you suggested on the prongs in the plug, though even those don't seem to jibe with the standard color wires. Is that a test I can run with the tank off and no power to the circuit?

The only white four prong connector like the one in your picture that I have found is in the relay box, and is not attached to a plug. The wires going into it are brown, green/purple, red/yellow, and green/brown. Don't know what the function of this would be.

Thanks again.
  • Minnesota
  • 1985 K100RS

Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #17 on: June 23, 2015, 02:04:59 PM »
Rbm, I'm getting 600 ohms between the ground prong (which I'm assuming is the one the dark brown or black lead connects to in the sensing unit) and two of the other prongs--one with the two grays, and one with the purple wire.  I also found a cutaway photo of this sensor online that shows a red wire, so maybe I'm dealing with the original part.
  • Minnesota
  • 1985 K100RS

Offline rbm

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #18 on: June 23, 2015, 03:18:15 PM »
  Maybe this is the original version that was changed on later models?
Correct.  This version uses thermistors that get cooled by the fuel when immersed and heated when exposed to air.  The circuit board in the instrument cluster understands how to interpret these temperature differences and turns on/off lights on the dash.  The circuit is attached to this post.

Quote from: rogan
  The two gray wires look like they join to one of the four prongs.
These would be the common connection between the thermistors which would be connected to ground.


Quote from: rogan
Perhaps I could try to run the test you suggested on the prongs in the plug, though even those don't seem to jibe with the standard color wires. Is that a test I can run with the tank off and no power to the circuit?
Yes, you can do that.

Quote from: rogan
The only white four prong connector like the one in your picture that I have found is in the relay box, and is not attached to a plug. The wires going into it are brown, green/purple, red/yellow, and green/brown. Don't know what the function of this would be.

Thanks again.
This is the optional alarm connector. Green/purple is actually green/gray.  Age does strange things to vinyl.  If you want, you can repurpose that connector if you feel you will never need the alarm function on the motorcycle.

If you are not already aware, a full colour schematic for the early RS/RT can be found on my Google Drive.
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #19 on: June 23, 2015, 03:42:10 PM »
Rbm, thanks again.  If I did the Ohm test correctly in my previous post, it seems like the sensor itself may be good. Inge says that my blue plastic circuit board is a later one that will not  work with the 7L light, but I'm wondering if I can get it to work with the 4L light.  I doubt I'd ever use the alarm connector, so I like the idea of being able to plug it in properly to the sensor prongs.  I'd have to be careful to wire the leads from the alarm connector to the downstream wires properly and label them so it the color scheme isn't so confusing.

Do you think it's feasible to get the 4L light to work in this fashion?

Thanks.
  • Minnesota
  • 1985 K100RS

Offline rbm

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #20 on: June 23, 2015, 06:12:20 PM »
There are two sensors so make sure you test both.

I would not suggest trying to rewire the alarm connector.  Rather, clip the connector off with some leads remaining, long enough to splice into the existing harness wires.  You'll be splicing and soldering the connector to the harness wires, then covering them in shrinkwrap tubing to insulate them.  That means you'll need to positively identify the corresponding connections on the sensor assembly, so take your time doing that.

It shouldn't be hard to get the 4L light to work.  If it is going to work at all, once you connect the thermistor and ground, the light should illuminate (with battery power applied) because the thermistor will be in free air.  Take time to conduct these tests before buttoning up your work.
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #21 on: June 23, 2015, 11:08:09 PM »
Quote
There are two sensors so make sure you test both.

That's what I was asking in my post#17.  I got readings of about 500 ohms when I retested with a different meter from two of the prongs, the one with the double gray wire and the purple one, assuming the brown wire is the ground.  Is there something else to test?

I wasn't going to rewire the alarm, just use the connector. I may use Posi-lock connectors with shrink tubing instead of soldering, we'll see.

Quote
It shouldn't be hard to get the 4L light to work.

I'd certainly like to think so!

Thanks again.



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Offline rbm

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #22 on: June 24, 2015, 06:29:31 AM »
Thermistor configuration inside the sender:


And the associated schematic, showing the two thermistors T1 and T2:
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline rogan

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #23 on: June 24, 2015, 12:17:19 PM »
Rbm, sorry, I think I need a simpler explanation.  My electrical knowledge is rudimentary at best.

Are both thermistors attached to (or part of ) the red wire that your arrows were pointing to on the cutaway photo?  I checked the resistance between the pin connected to the brown wire, and the pin connected to the red wire, and I got 1200 ohms.  If both thermistors are on that circuit, and each have 600 ohms resistance, then it would seem that they are working properly.

If your arrows were pointing at something else in the photo that I can't check at the pin connectors, then it would seem that I have to open up the plastic sensor sleeve to get at something inside.  I see a seam in the plastic, but I'm not sure this will come apart without destroying the sensor.

I could use some clarification.

In the meantime, I think I'll put the cluster back together enough so I can run some jumpers from a 12v battery to the cluster pin #6 for power, and a jumper from the red wire prong on the sensor unit to cluster pin #7 (the 4L light), and a jumper from the brown wire pin on the sensor to pin #13 on the cluster for a ground, and see if I find any joy. Maybe all the sensor pins need to be connected somewhere for the light to come on?  If anyone has a better suggestion for a test, please let me know.

Thanks again.
  • Minnesota
  • 1985 K100RS

Offline rbm

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Re: 1985 K100 RT Instrument Cluster Removal
« Reply #24 on: June 24, 2015, 12:27:55 PM »
If you measured 1200 ohms, you have accomplished two tasks:
1. proved the thermistors are correct at the appropriate temperature
2. identified the two connector pins that correspond to one end of EACH of the thermistors (pins T1 and T2).  Now all you have to do is identify the pin that goes to the common connection (pin 31) aka. ground.
The easiest process at this point is to use an ohmmeter to identify the pin that corresponds with the fuel pump's purple lead (pin 15).  Once you identify that pin, the only remaining pin must be ground.

Don't open the sensor.  I was only annotating your photo to show you that two thermistors exist.  Take my word for it; yours does also.
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

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