Testing fuel level switch

Hey all, I just got my “new” fuel level switch for an 81 Kz550 C. I did some measuring and the book was too vague to give an accurate testing procedure for this device. I hooked my meter leads to the wires and got “1.650/1.700 kilo ohms. The book said it should read 117 ohms, but doesn’t specify whether the switch should be tested while connected to the gas tank (filled up) it not. I’m testing it dry right now.
The trouble is, I can’t test it while attached to the gas tank because I’m currently stripping and coating the inside with liner so gas filled isn’t much of an option for at least a week. Just wanna know if this part is good or not. Any help would be appreciated it! Thank you 

The manual for the 1000/1100 says 
Full (highest position)   0.5 - 5.5
Empty (lowest position)   102 - 118

Tested on the bench with the switch out of the tank.

So if mine is similar, than my sensor is way above the threshold at 1.7 kiloohms

Are you sure that the connectors you connected your ohmmeter to were really clean and that there are no breaks in the wires? That reading does seem crazy high.

You could connect the new fuel switch to the wire harness, turn the ignition switch to ON, then see what the low fuel warning light does. This test would simulate an empty fuel tank. The owner's manual should have a description of the device's function. I think the one on my bike is the same as yours or nearly so. I did the test with a NOS fuel switch (engine off) -->> the warning light glowed within about 30 seconds.

Resistance values & info from my notes. tests done using a VC97 digital multimeter:
Stock fuel level switch on bike, fuel tank full of gasoline & switch submersed in fuel = 4.4 k ohms (Bk/W wire & Y/Bk wire).
I've never tested the resistance of that fuel switch in air or when the tank was empty.
NOS fuel level switch (27010-1096) = 1.2 k ohms in air (black/white & yellow/black wires).
(1.28 k Ω @ 76F & 1.22 k Ω @ 88F, so the resistance goes down the warmer it gets. I think there's a thermistor in the little can.).
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PO cut the wires when he put on the new tank, ill just be buying single connectors from the electronics store and connecting them that way. So a corroded connector could be part of the issue. I polished up all the connected parts i had access to and got it down to 1.45 k ohms. may just need a little more TLC to get it down to 1.28 in air, ill check it again when i have the tank all together. if worse comes to worse, ill use it as a plug and gauge low fuel by bike sputter lol. 

On a side note, I love how scientific you are in every post Martin. Its really helpful to have all the information

Just connect the fuel switch & see if it turns on the warning light. engine off or engine on. either way should work.
I don't know what the KZ650 resistance should be, but using my numbers as a reference, 1.45 k Ω might be close enough, I guess. ???
Did you check the harness voltage? There's a test in the 81 KZ650 manual for checking that.


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Unless I'm missing something the sensor should detect two conditions: wet or dry.  As martin mentions, you should be able to test dry outside the tank and the light should turn on.  To test wet, dunk the sensor in a cup of gasoline and make sure the light goes off.  Don't think you need the actual gas tank for testing.

Yes. It's pretty simple. I'm pretty sure there's a thermistor inside the little can. Voltage warms it up but the gasoline carries away the heat, keeping it cool. So, obviously when the fuel gets low, the thermistor warms up enough to allow electrical current to flow & complete the circuit to the warning light. I guess that's how it works.


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thats a pretty smart way to make a switch, i'm impressed haha