Low Fuel Light Bulb Breva 750

[antmanbee]

On a Breva 750 is the low fuel light supposed to come on when you fist turn on the key as a check?
If not, does this mean the bulb is burned out or are there other possibilities? The light has never worked on this bike since I purchased it used.
The circuit outside of the dash looks simple. It is just a thermistor in the tank with a line in and out from the dash.
I have found no information on what goes on inside the dash.

[Wayne Orwig]

On a Breva 750 is the low fuel light supposed to come on when you fist turn on the key as a check?
If not, does this mean the bulb is burned out or are there other possibilities? The light has never worked on this bike since I purchased it used.
The circuit outside of the dash looks simple. It is just a thermistor in the tank with a line in and out from the dash.
I have found no information on what goes on inside the dash.

No 'test' function.

The thermistor is about 1200 ohm at room temp.

Nothing in the dash but a bulb. Short out the thermistor and the bulb should light.

[antmanbee]

Thanks Wayne.
I have some of these thermistors to use if the Breva one tests bad. It is 2K ohm at room temp.
Digi-Key Part Number   480-3340-ND   
Manufacturer   Honeywell Sensing and Productivity Solutions   
Manufacturer Part Number   135-202FAG-J01   
Description   THERMISTOR NTC 2KOHM 3468K DO35

[Wayne Orwig]

Well, I'm thinking:

I suspect that you need a lower resistance, to generate the heat, that starts the process where it self heats and lights the bulb.
I can't find a single bit of info on the wattage of that thermistor. That looks like about 1/4 watt. The one in the tank is large, closer to 1 watt, to pass that bulb current.
The one in the tank is enclosed in a shield, in case something goes wrong in the gasoline, it is less likely to be a safety issue.

Have you tested the bulb?

[antmanbee]

No I have not tested anything yet. I am going out to ride it now but I will probably pull it apart enough to test it tomorrow or Tuesday.
That is the thermistor that someone in the Ducati forum used to fix his low fuel light issue.

[antmanbee]

See post #30 in this Ducati thread for how he did it.
https://www.ducati.ms/threads/ran-out-of-fuel-twice-no-fuel-light.132039/page-2

[Kiwi_Roy]

Well, I'm thinking:

I suspect that you need a lower resistance, to generate the heat, that starts the process where it self heats and lights the bulb.
I can't find a single bit of info on the wattage of that thermistor. That looks like about 1/4 watt. The one in the tank is large, closer to 1 watt, to pass that bulb current.
The one in the tank is enclosed in a shield, in case something goes wrong in the gasoline, it is less likely to be a safety issue.

Have you tested the bulb?

The sensor Wayne mentioned is made by Panasonic. the thermistor is enclosed in a metal can with a very fine slot to allow the fuel In/Out, I was able to purchase a couple, one I used on an early Triumph the other I used on a Guzzi, I will try to find the part No but I wouldn't hold out much hope of finding one to purchase.
Typically they either work or not, Measure the resistance with your meter or short the wire to chassis to test the lamp. They would often get burnt out by mixing the plug with the one for an electric petcock.
LED lamps do not draw enough current to make the thermistor heat up, I have several times replaced the dash lamp with an LED but retained one of the incandescent lamps out of sight in parallel.

[malik]

On a Breva 750 is the low fuel light supposed to come on when you fist turn on the key as a check?
.......

I believe so. On the V7, all the dash lights cycle when the ignition is first turned on. I shouldn't think the Breva would be different, same ECU as the early V7, though the dash is physically different.

[antmanbee]

I looked at the wiring diagram for an early V7 Classic and it is very close to the Breva but not the same.
To the thermistor is one wire from the dash and the other wire off the thermistor goes to ground.
On the Breva both wires off the thermistor go to the dash. I assume 1 wire is for ground and it is grounded through the dash.
But no telling without a dash diagram.
Big block Guzzis like V11, EV, Jackal, I am pretty sure it is like Wayne said and has not test function.
But is there anyone with a Breva 750 that can confirm that if the key is turned on and the dash does it's sweep that the fuel light comes on briefly?

[Dharma Bum]

On my Breva it comes on "occasionally ".

[malik]

Just spoke with Gonzo. On his Breva, the low fuel light does NOT cycle on initial ignition. Although it does come on sometimes, then fade out without fuel being low - and that's on an 8,000 km bike.

[antmanbee]

On my Breva it comes on "occasionally ".

I don't understand. Do you mean in general use while riding it comes on occasionally?
What I want to know is when you switch on the key and the dash needles sweep and the dash lights come on, does the fuel light always come on briefly too?

[antmanbee]

Just spoke with Gonzo. On his Breva, the low fuel light does NOT cycle on initial ignition. Although it does come on sometimes, then fade out without fuel being low - and that's on an 8,000 km bike.

Thanks, that's kind of strange to have that inconsistency.

[Kiwi_Roy]

Here is a replacement for the thermistor in the V11 Fuel tank, Panasonic part No is ERTLG12N7
Oops this is only for a dash with dedicated light bulbs, not for an electronic dash with stepper motor speedo etc

http://industrial.panasonic.com/lecs/www-data/pdf/AUD0000/AUD0000CE2.pdf

I tried contacting Panasonic without success but found them on a Chinese site N Gate for $15, I ordered a pair, they took
about 2 months to arrive, I think they were shipped by boat.
 
It's not a direct replacement you will have to adapt the holder somewhat but for $15 instead of $150+
 
Its a direct replacement for the one in my friends old Triumph Tiger.

Here we go with the data sheet
https://static6.arrow.com/aropdfconversion/599d112d4eefad38687211b895992cc0102dc8b9/aud0000ce2.pdf

I wouldn't be at all surprised if you are unable to find these to purchase, I had enough trouble 3 years ago, I suspect someone is trying to corner the market, many automobiles use this sensor.

[Kiwi_Roy]

http://www.thisoldtractor.com/guzzi007/schematics/2004_750_Breva.gif
The Breva schematic shows an in tank pump and sensor (10), its anybodies guess what this is, at first I thought it would have a float switch for the electronic dash but I have been wrong before.
They do use the same symbology for (10) and (45) which would be a thermistor for sure.
If it is a thermistor I don't think it would be possible to mix up the connector and burn it out as happened so often on the Californias.
I agree with Wayne, if its a thermistor it would need to be < 1k to start heating up and it should be enclosed like the Panasonic, a thermistor will glow white hot if its fed 12 Volts and not covered in fuel.
https://static6.arrow.com/aropdfconversion/599d112d4eefad38687211b895992cc0102dc8b9/aud0000ce2.pdf

[antmanbee]

I found a picture of the Breva 750 pump assembly and the sensor looks like a thermistor in a can which is typical for the submersible pump assemblies.
The blue and white wires go back to the dash.

[antmanbee]

Well I have 10.9V across the two wires that go int the dash. If I short them I still have no low fuel light.
I have 2.5K ohms across the two wires going to the thermistor which is submerged in fuel.

[Kiwi_Roy]

Do the other lights cycle when you turn the key On?
The dash doesn't have replaceable lamps, just LEDs soldered to the board.

[antmanbee]

Yes all the other functions and lights of the dash work.

There is one other thing odd and this may be normal but I have no way of knowing as I have only experience with this one Breva,
but the hazard light switch on the dash is lit up all the time while the bike is running or if the key is in the on position.
The hazard switch/light will flash on and off if turned on.
Is this normal? It seems to me it would be better not lit up as the default and only flash when turned on.

[Wayne Orwig]

Does not come on with the key that I recall.

[antmanbee]

Does not come on with the key that I recall.

Wayne,
Are you referring to the Fuel light or the Flasher warning light?

[Wayne Orwig]

Wayne,
Are you referring to the Fuel light or the Flasher warning light?

Sorry, fuel light only came on with low fuel.

I'm not certain on the flasher light.

[hzbloke]

On my '08 Breva the fuel light only comes on when the fuel is low, not on startup. The red hazard light is on the whole time the ignition is on.

[Kiwi_Roy]

I wonder if there is a delay on the low fuel light, you would expect it to come on if the sensor wires are shorted together.
I have a dash here but I need to get a cable so I can connect to it.

[antmanbee]

With having shorted the 2 wires to the dash and no light while shorted, there is my problem.
So the question for me is, will it be worth the risk of dash disassembly of a otherwise fully functioning dash to possibly fix the light.
From reading more from the Ducati thread it looks like there is a 116 ohm resistor in series with the thermistor. So there are other possible faults besides the LED.

This info is from the Ducati thread,

First how it works : The thermistor is a device which changes resistance with temperature, with resistance dropping as temperature increases. As it is a resistor, it generates heat, which in turn reduces its resistance, generating more heat etc etc... When the thermistor is inside the fuel, the heat dissipation to the fluid is high enough that it exceeds the heat being generated by the thermistor and hence its temperature is stabilized at a certain level. However, when the fuel is low, and the thermistor is in air, the heat dissipation rate decreases, such that the thermistor starts to increase temperature. The fuel light works by putting the thermistor is series with a set resistance in order to deliver a designed current to the dash when the thermistor resistance ( as dictated by its temperature) rises above a defined value.
Measurements : Using a potentiometer in place of the thermistor it was possible to deduce that the light will come on when the thermistor resistance is below 160 ohms. By measuring the voltage drop over the potentiometer at various values it was possible to deduce that on the bike the thermistor is in series with a resistor of 116 ohms. What has happened to my stock sensor was that it was still generally working, but did not drop resistance far enough, hence the light did not come on.
Challenge : need to find thermistor which will provide the correct characteristics : resistance in fuel > 160 ohms, resistance in air < 160 ohms, but beyond this must have high resistance in fuel to avoid big constant current draw, and must be such that it doesn't go unstable ( heat up excessively) when exposed to air. Thermistors are defined by their B value, but generally also share their dissipation constant in air, and the current they will accept. Using this it was possible to build a system model, calculating resistance and hence heat generation, as well as the heat dissipation rate when in or out of the fuel. Of course, it is also somewhat important to make sure that the thermistor in air does not exceed the fuel auto-ignite temp, or the max temp permitted by the thermistor.
Result : using published properties, and knowing something of the application, I was able to select the Honeywell 135-202FAG-J01 with B value 3468K and dissipation in air of 2.5mW/degC. The nice part of this thermistor is that it is glass encased, and hence not affected by the fuel as I suspect the stock ones are. Cost was a whopping $1.47 a piece.
Testing : Bench testing was completed with 12v and a series resistor of 116 ohms to confirm that the thermistor selected responds as expected, and then I fitted it to the bike ( but not in the tank) and confirmed function by testing in and out of fluid. The fuel light worked as expected. As the worst case for the thermistor is when it is dry, I ran the thermistor in air for 24 hours constantly, and all seemed fine. However, this is as far as I got and never fitted the thermistor to the bike. I will when my light fails next time. To fit it, I'll need to dismantle the stock sensor, and fit the new thermistor in place of the old one.
BTW - note that the thermistor is mounted inside a can which has only small holes in it, such that the thermistor response is slowed and the light doesn't go on/ constantly when the fuel level is near the switch level.

So that's the status - the design is done, but not yet tested. Try it at your own risk !

[Wayne Orwig]

The other models that I owned, the EV and the Centauro, that use that same thermistor, did NOT have a resistor also. It was a simple thermistor and bulb, nothing else.

You shorted the wires, and the bulb did not light. Bad bulb or wiring, right?

Sounds like you are itching to replace the thermistor anyway, even though the bulb does not work.

[Kiwi_Roy]

The small holes in the can are not to damp the fluid, If the sensor receives full 12 Volts in air the it can get white hot and fuse, any flame is cooled passing through the tiny holes so its contained inside the capsule. That's why you cannot use a bare thermistor.
If the light doesn't go when you short the wires out do you think a new sensor will fix it?
The dash I have is not screwed together, the light is a surface mount LED, when I find another ribbon cable I will check it out.
I think the 2.5k resistance you measured may be ok although I expected it to be lower.

BTW, is the text on your screen extra wide, (on my Mac it disappears off to the side) I think its caused by the reference in the 3rd post setting the text width

[antmanbee]

The other models that I owned, the EV and the Centauro, that use that same thermistor, did NOT have a resistor also. It was a simple thermistor and bulb, nothing else.

You shorted the wires, and the bulb did not light. Bad bulb or wiring, right?

Sounds like you are itching to replace the thermistor anyway, even though the bulb does not work.

I am not itching to replace anything. I wish I had the luck to only have a bad thermistor because it looks relatively easy and cheap to repair.
I was including all the pertinent information I had found about the thermistor repair because I think that a thermistor failure is probably more common.
The little 'thermistor in a can' seems to be on most of the internal pump/filter assemblies from the Italian manufacturers.
I have seen it on my Griso and CalVin too, and in many photos of pump assemblies while researching.
I included the information about the extra resistor in series because the Ducati has an electronic dash like on most late model Guzzis and I thought it would be similar.
I would much prefer if all my newer bikes had the gauge and warning light set up of the EV or Centauro.
I hate the electronic dash with it's integration of key immobilizers, parasitic drain, key codes and links to the ECU.

[antmanbee]

The small holes in the can are not to damp the fluid, If the sensor receives full 12 Volts in air the it can get white hot and fuse, any flame is cooled passing through the tiny holes so its contained inside the capsule. That's why you cannot use a bare thermistor.
If the light doesn't go when you short the wires out do you think a new sensor will fix it?
The dash I have is not screwed together, the light is a surface mount LED, when I find another ribbon cable I will check it out.
I think the 2.5k resistance you measured may be ok although I expected it to be lower.

BTW, is the text on your screen extra wide, (on my Mac it disappears off to the side) I think its caused by the reference in the 3rd post setting the text width

I don't think a new thermistor will fix it. It seems to me that shorting the wires to the dash should turn on the light.
I would think that the value of 2.5K would not matter as long as the resistance drops down low enough when the thermistor heats up when exposed to air.
The new thermistors I have that are rated as 2K test about 1.65K.

The text wrap in post 3 from the hyperlink to the thermistor is what is causing the extra wide screen. I will remove the link and just put the part number in the post instead.

[Wayne Orwig]

I am not itching to replace anything. I wish I had the luck to only have a bad thermistor because it looks relatively easy and cheap to repair.
......
I would much prefer if all my newer bikes had the gauge and warning light set up of the EV or Centauro.
I hate the electronic dash with it's integration of key immobilizers, parasitic drain, key codes and links to the ECU.

On the early California's and a few others, with the external fuel pump, the fuel solenoid and fuel sensor plug were identical. It was easy to inadvertently mix them up. One had red paint on it, but still, they got crossed often. That would apply 12 volt solenoid power to the thermistor and it would of course kill it. I have heard of a few of the sensors leaking too. But I can't say I have ever heard of a sensor just failing. They are pretty simple and reliable.

Is your dash not like that photo I posted? I didn't know they had anything more complex on the 750 Breva.