I have an intermittant fault with the fuel gauge on my 2001 R129 SL.

When the tank is full the gauge doesn't register. When the tank gets down to 3/4 or less the gauge springs to life and works all the way down to however low I dare go.

I've had the sender unit out and cleaned the tracks with electrical cleaner. There is full movement available on the arm.

I used a multimeter to test the resistance at the plug and it went from 35 ohms (iirc) up to 70 ohms.

I connected the sender and tried moving the arm through it's arc expecting the fuel gauge to react at some point but it didn't.

I am convinced it must be a faulty sender unit. Is there anything else I can test ?

 

Same issue happened with my 95. New sender cured the issue. Good luck...