Trying to due some PM work

That rear one is for a temperature sensor. Use the one on the front on the side. It’s about in the center of the axle.

 

OK, I won't get into the owning the truck bit but here is what you need to know.

The bottom plug is for draining the oil, the middle plug is for the temp sensor and the top one is for the fill.

Opps, Dave posted before me.

 

Isn't the side where the sensor goes?

You fill it up that high and you get a ton of oil when the axle is pulled.

I've seen axles pulled and there usually isn't much oil that comes out.

Where's the wiring for the sensor?
And where's the sensor at?

 

Yup - got me.

Top - fill
Middle- temp sensor
Bottom - drain.

Stick yer little finger in the top one and feel around like a teenager, and if it gets all wet and stinky - (because that stuff does stink),

Then button her up and take her to work.

 

Probably didn’t come spec with a sensor.

Angle of photo is deceiving - should be at a level to bathe in oil.

 

The sensor needs to be in the oil, so it would be installed in the middle hole.

The upper hole is the fill/level hole. On a truck with air ride I've always filled the diffs with the suspension inflated. Most air ride suspensions will cause the diff to pitch forward when deflated, which would cause the fill hole to sit higher.

Plus the diff and the wheel ends share oil, so you want the oil level in the diff to be high enough that oil can trickle its way down the axle tubes to the wheel bearings. The upper plug should set the level to roughly the bottom of the axle tube.