Deleting TC
From what I've read, a 3 channel rear only has one sensor on the differential/carrier housing and the reluctor ring is actually inside the pumpkin (I haven't actually checked it out myself, but I would guess you just look for a single harness/wire plugging in somewhere on the pumpkin). A 4 channel rear as an ABS sensor on the end of each axle tube, one for each wheel (in which case I assume you'd identify it as such by looking for a split harness/wire running to each rear wheel).
Hope that was helpful
-Josh


