So, the brake light is lit on my dashboard. The computer reports "PAO", which seems to actually be PAD, so I guess I need new brake pads. I will be fixing some other things as well, listed below.

I'm planning to order a set of front and rear pads for my car, but going to RockAuto I'm having difficulty choosing the correct parts...
- For the front pads, I see mention of "without ATE caliper"
- For the rear I see a .525 and .655 measurement. What is this referring to?
- I will be ordering new wear sensors as well, or do they normally come in the box with the pads? I assume not.

The wire is broken off on my oil pressure sensor, but I'm not sure where it's located on my 4 liter engine. Where can I find the sensor?

When I do a search of my VIN (SAJHL1941LC6xxxxx) online, I'm told that I have a Sovereign, but the round sealed beam headlights indicate that it's a Base model and I don't have any Sovereign badging. How else can I tell what I really have? Are there any options specific to the Sovereign?

I have a single wiper blade that does the whole windshield, not a pair that do left and right... everywhere online lists them as 21" left and right. What is the correct size?

This is a 1990 XJ-6 (XJ-40) with 4 liter engine.

 

Ok, well yes PAO is pad, so you need some new brake pads. In Rock Auto, hit 1990 Vanden Plas and take your pick, get the ones with sensors or get the sensors independently. Some pads list Vin fitments, no experience with those, I generally get the cheapest as they last about 50,000+ k anyway unless you're a brake hog.
If your vin says you have sovereign trim then that's what you have. Ignore all other info sources.

The XJ40 has only one wiper blade so get any one listed. As shipping is mainly the cost of this stuff, not a bad idea to buy multiples as shipping doesn't go up much overall.
I just got some wholesaler clearout oil filters for a buck fifty a piece with about 20 bucks shipping, so I bought a few.

The oil pressure sender is on the left side of the motor, down by the filter under the manifold best got to from under the car.

Larry
ps. part numbers are easily researched here:

https://parts.jaguarlandroverclassic.../brand/jaguar/

 

Thank you very much for all the useful information. It will be quite helpful!
I hadn't considered buying spares now to avoid shipping. Great idea when shopping at a place like RockAuto.