I see my 2WD '94 F150's differential has an electrical connection going to the top. What does this do? I'm looking to change the 3.08 gears to 3.55 or 3.73 for towing, what considerations are there related to this connection? I assume if I look for a compete rear instead of changing internal parts I need to find one that has that connection?

Thanks

 

That's the rear differential ABS sensor. It's positioned above the ring gear and monitors the gear's rotation.

Any axle out of any truck with ABS will have the same sensor.

 

On some models they also use that sensor to detect vehicle speed.