ABS rear put into non ABS rear truck: vehicle speed sensor location?

Hi,

My mechanic is replacing the original rear in my non-ABS 2nd gen with an ABS rear that I sourced. There's a sensor on the ring gear on the original axle that doesn't exist on the new ABS axle. I'm hoping this isn't the VSS so my speedo will still work w/ this new axle but hoping somebody could confirm or even tell me what this thing is?

Thanks!

 

On my truck with the manual, the speed sensor is on the transfer case.