Car Fuel Gauge or Fuel Pump?

hI,

I have a Mercedes C180 Avantgarde 2013


When ever I top up fuel the gauge will show me its 1/4 full no matter how much I top up .

Wanted to check the resistance by add a resistor to increase/reducing the level on the gauge in order to do a sending unit check.

But my there are a lot of wire connecting to the fuel pump hence hindering me from doing.

Hope this picture will help to identify the 2 wire that i should work on.
Please help.

Thanks!



I didn't find the right solution from the Internet.



References:
 www.cnet.com/forums/discussions/car-fuel-gauge-or-fuel-pump/

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