While replacing the fuel pump on my '92 D150 I noticed for the first time a two wire connector plugged onto what appears to be a sensor located in the topside of the differential. Having never seen it mentioned in the section on sensors in any of the books I've referenced, I was quite surprised. It also isn't shown in any of the wiring diagrams I've found. The wire colors are red and blue. My gut feeling is that it has something to do with the anti-lock brake system. I'm hoping someone can shed some light as to what this dohickey is.

 

ABS Wheel Speed Sensor

 

that is the ABS wheel speed sensor, however i just looked on the wiring diagram for my '90 W150 and it says the wire colors should be red and white. none the less, thats the only sensor that would be in your rear diff

 

Thanks. I know its an old truck but I keep learning something new about it all of the time. By the way, it cranks and runs a whole lot better with the new fuel pump. I would not have thought that it would make that much difference.