Author Topic: K75 Fuel Light / Sending Unit Question.  (Read 416 times)

Offline 3dognate

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K75 Fuel Light / Sending Unit Question.
« on: April 15, 2022, 10:35:43 PM »
This has probably been answered before but I can't find it.

Problem: The fuel light stays on

I have an '87 K75 that I'm refreshing. I Installed a new fuel sending unit from EME in it (Part no. 62 16 1 459 565), I've verified that it's the right part for my year bike, and that the float arm varies in ohms from 103 ohms all the way down and 10 ohms all the way up. From the wiring diagram I'm not sure how to troubleshoot why the light stays on. I've reached into the tank and manipulated the arm and the light is always on.

Any tips on what might be the issue given the sending unit is new and appears to be working? Something in the gauge cluster? Doesn't appear to be any relay in the circuit.

I just did another '87 K75C with the same fuel sending unit and it works perfect.   :idunno:



  • Illinois
  • 1987 K75c Henna Red / 1987 K75 Black

Online Martin

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  • Posts: 4344
Re: K75 Fuel Light / Sending Unit Question.
« Reply #1 on: April 15, 2022, 11:30:54 PM »
On some senders there are two different systems in the sender. One wiper arm runs along the windings and operates the fuel gauge. The other separate wiper is just a on off for the fuel light. There is also a timer built in to stop the fuel light flashing on and off with the fuel sloshing in the tank. It takes around 30 seconds with the float low enough to activate the light.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline rbm

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Re: K75 Fuel Light / Sending Unit Question.
« Reply #2 on: April 16, 2022, 07:28:02 AM »
See my article "Messing with the In-tank Fuel Sender" over on the other forum.

There is some short circuit between the low fuel circuit on the sender and ground,  Separate the fuel tank connector from the harness and use an ohmmeter to test for a short between White and Brown on the tank side of the connector, and then on the harness side.,
  • Regards, Robert
Toronto, Ontario

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

Offline frankenduck

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Re: K75 Fuel Light / Sending Unit Question.
« Reply #3 on: April 16, 2022, 09:40:34 AM »
Could be a bad fuel level sender. Since you have another K75, I'd swap tanks to see if the other FLS works on the subject bike.
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Offline 3dognate

  • Motobrick Curious
  • Posts: 12
Re: K75 Fuel Light / Sending Unit Question.
« Reply #4 on: April 16, 2022, 10:25:27 AM »
Testing for short between the brown and white wires put me on the right path along with RBM's article.

It was working just fine. I was expecting the light to go out when the arm was raised. The silly delay circuit was tripping me up. Turns out if I held the arm up the light would go out after 20-30 seconds.

My first K bikes. :)
  • Illinois
  • 1987 K75c Henna Red / 1987 K75 Black

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