Fuel Guage/sending unit

[Giro]

After looking through my Ford repair manual and these forums, i still havent found what i need, so im resorting to asking...Is there only supposed to be 1 wire (the yellow one) that comes out of the fuel level sending unit? guage always reads low, and the previous owner upgraded to a 255 lph pump, and he told me that when he changed it, the guage was reading low, seems like a coincedence, i suspect wiring issues.

Anyways, there is a black and red wire coming down from the harness to the fuel pump, and a yellow wire going to the fuel level sending unit, but the harness is a 4 wire harness, so there is 1 that has nothing (there is a wire going to the harness, but inside the fuel pump assembly, the prong thingy is empty).

I know cars, and i know those potentiometers work, by taking the supplied constant voltage by the pcm, modifying it, and sending it back, so it seems like there is a ground wire missing (the empty one) can someone please confirm this for me? thanks for your time.

[Giro]

here are the pictures

[BLOWN38]

Pretty sure you are missing the wire inside.

[Giro]

thats what i am thinking, but i cannot seem to find anything to confirm that for me. no pictures in the repair manual, and i searched and couldnt find anything on the forum.

[BLOWN38]

Just came across a picture of mine and do NOT have a wire in the same spot.

fuel sending unit pic