Fuel low lamp

[Norman Golm]

The fuel low lamp socket has a dropping resistor built into it, my question is the resistor incorporated in the design to reduce the intensity of the lamp or to make the contacts at the fuel level sensor intrinsically safe, meaning the arc is below the energy level to cause a spark and ignite the fuel vapors?

[Duncan M]

Hi Norman-
My understanding is they did it for the safety reason firstly. When the fuel tank first fills with gas, the sensor (where the electrical contacts are) fills up with gas through little holes on top. When the fuel level drops low, the arm drops and the contacts meet and the light goes on, but fuel does not ever drain out of the sensor-- no matter how low the fuel level gets. For those that did not know, sure enough, the electrical contact for the low fuel warning light is made in gasoline. But, as Norman says, after the electricity has been knocked down by the resistance built into the lamp unit.

The sending unit, or sensor, keeps an electrical contact arc away from any vapors in a low fuel level condition in the fuel tank, by being a sort of little, always full tank, within the actual fuel tank.

Let it sit long enough with the fuel level in the gas tank below the sensor, and I suppose the gas in there (sensor) would evaporate and get stale and gunky. When the tank is fuller, I suppose the gas in the sensor stays fresh by intermingling with the fuel in the tank, through those little holes.
I think..
Duncan-

[Marv]

Has anyone ever made present day technology improvements to that method of making and breaking contacts through a gasoline medium?

Marv TC5141 "Lady Di"

[dirk w dondorp]

For an explosion in a gas tank caused by the sensor you need a certain minimum- lean- mixture of gas and available oxygen- In a "rich" fuel suround it is hard to ignite!

[Marv]

Aware of that fact Dirk, but that was not my question.

[dirk w dondorp]

Marv, was meant as an answer on the original question.......

[Duncan M]

Marv-
I don't think there is any reason to try and improve the low fuel sender, that makes contact within fuel. It seems to work just fine, along with looking into the tank with a flashlight Some have made measuring sticks, using marks along the length to indicate amounts of fuel.

[Steve Simmons]

I use a flashlight primarily because I don't want the stink of the dipstick getting on my luggage! Even using a metal one requires a rag to wipe it off, and then the rag stinks.

And to the original question, I haven't seen any changes to the design other than a "better" seal.