RE: gear oil in the rear end differential of a 89 XLT Ford Ranger?
I found where to add the oil. It is not at the top as I thought it would be. It is a pug not a bolt. It is located on the front of the differential about one-third of the way from the bottom on the driver's side. I will add it tomorrow. It looks like you use a ratchet to fit in the plug cavity to turn it.
That hole is also the correct level of oil.