I'm looking to utilize the stock sending unit to display a fuel level % on the MXL. Can someone explain how it works? I've got a yellow and black wire which lead to the sending unit. Id guess the yellow gets 12v and the black is sending a range based on the float level? Blue/red is pump positive and black is pump negative.

 

I think yellow is signal, black is ground and red/blue is power, but I'd check the wiring diagram if I were you. You'll need a resistor between power and signal to generate an output voltage.

 

Ground the Black and run the Yellow to your signal input in the fuel gauge if it can work off of just a resistance signal. If it needs a positive signal, then you will need to add a resistor, like Pat said. The other Black and Blue/Red power the fuel pump.