TOPIC:

Yes, it sounds interesting, but I need to understand how the current set up works. I thought of some problems with it, i.e. if it works on temperature change how does such system work in summer or winter or when the fuel is cold and gets warmer with the engine radiating heat? But I think I have a go, but as I said I need to wind out a bit more.
I have measured the resistance on a sensor which I have from the old tank. I get 3kOhm when at ambient temperature (about 20degr) and it go down to 2.2kOhm when I hold it against a light bulb which I would guess increases the temperature by maybe 20degr.
This is the sensor or switch:

Well I don't know if that is a Thermistor. Although the system does work on resistance, I don't know how that would function just on temperature. Try checking the resistance, while immersed in fuel at different levels.
I think it will change resistance as it gets covered then uncovered with fuel, maybe other liquids to. But I don't know what type of resistor that is. Just varying the resistance to ground, so limiting the current to the bulb, it would first come on dim then get brighter.
I doubt after years of being in a fuel tank, there are any Identifying marks/ numbers on the resistor element?

I have asked the person who sells the thermistors on ebay how to test it and in his replay was this information:
To test the sensor you have to make sure the gas in the tank is below the sensor tip. The sensor lights the bulb when it has no gas touching it. It is cooled by the gas, so when gas is around it, it will not make contact inside.
So it is just a straight forward on/off or low and high resistance when the fuel is belowor above the thermistor level. This is what I measured and this is what I need to get my gauge showing the right information. C (cold) is empty and H (hot) will be for full.

I know when parking my bike after a run, it sits there and the fuel vaporizes. Coming out the tank vent in the cap with great force. Sitting right above that hot motor, you can feel the heat in the Tank, fuel included. Seems like the fuel its self would go through a wide temp swing. But I guess that the resistor works that way, as they seem to be used in several applications, for the low level switch.
How many are you going to Series together? Will that give you a contact through them, or if one is out of the Fuel, will it be an open circuit? I'm just wondering why the Manufactures don't have something like this set-up, so they would have no moving parts. Cost?

I just did a quick calculation, but I am not sure if I ever get components to fit. I also have not taken any other influencing factors in to account such as temperature changes due to hot and cold weather.





You commented:
I'm just wondering why the Manufactures don't have something like this set-up, so they would have no moving parts. Cost? Maybe it is because it does not work????

I found an interesting fuel sensor from a Harley Davidson, wonder how they work and if it is easier to adapt them for what I want to do?

That Hardley one looks interesting. But also it is quite large on the Length and the Threaded fitting.
I suppose there are many different designs out there.
It will be interesting on what you find out experimenting with this. On my bike the float bounces with the fuel, so it does not have a steady reading, it moves around at least a 1/4 of the scale. Sometimes more. I've soldered the ground connection where it was slip spade terminal, cleaned the contact and wire wrap, checked the resistance. The gauge is mounted well, terminals are tight.It reads fine till the level starts to drop, so I know its sensor related. Maybe your configuration would provide a rock steady reading.

Never thought trying to get some a bit special electronic components is so difficult. If you don't want to buy a container load from China nobody wants to know. I finally found a place which used to be a shop I went to when I was younger, which is now on-line and ships the components. Not cheap, but at least I am able to get something which I can use. So the thermistors are on the way and I hope it will give me at least some results to work from. I found a thermistor which has 3 Ohm @ 25deg with a positive coefficient, i.e. increases in resistance when getting warmer. This is what I need when the fuel does not cover the thermistor cooling it down.

My thermistors came yesterday, but I ordered the wrong ones. So I will need to wait for the replacements.

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I now got the right thermistors and I have linked five of them in series. Although they do what they suppose to do, but the temperature required for them to increase the resistance to about 20 to 25 ohms is so high I am not sure how to heat them up that much. I had to use a hot air gun to get the meter registering the resistance increase. In order to get the thermistors up in resistance a very high current must flow through them. Unless the low level check switch is doing the trick here I am not sure if it will work.

So I am back to the same question: What is the Low fuel level check switch doing and how does it work?

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There is a chap on ebay selling thermistors for the fuel sensor in the tank. it is the one with the little metal cylinder mounted on a 4inch long piece of metal as the picture in the previous post shows. He sya the fuel keeps the thermistor cool (when submerged) and it heats up when the fuel level exposes the little cylinder with the thermistor in it. Somehow the fuel check switch, which is located under the battery behind the right hand side cover (on mine) does something to make the thing work. Just deeding 12V from the battery over the thermistor is not enough to heat it up. I don't think the fuel is completing an electrical circuit.