Unit Behind HPOP

Hey People, first of all, since this is my first post, I'd like to thank you ALL for the helpful and knowledgeable info you have provided me in the past with multiple issues. I've been a lurker until now. Kinda sounds nasty... Anyway, I have an issue that searching the forum hasn't help solve this time. In fixing a leak with the FRP sender on my 96 250 I realized that whatever is hooked to the back of what I believe is the HPOP is loose. It is located on the driver side of the filter housing down at the bottom in the valley. It appears to slide on a shaft coming out of the back of the HPOP and has a 2 wire connection and looks like it is held in place with a sleeve and a nut. The nut is gone so whatever it is slides back and forth. I recovered a flanged sleeve out of the valley but couldn't find the nut. I just cleaned the valley out with degreaser and hot water to find the fuel leak so it's possible I washed the nut out of the valley. The truck appears to run OK so I'm at a loss to figure out what this thing does. Thanks in advance for any clues....