I've just had my 1999 XJR ex Jaguar Test car - they shipped from Browns Lane Coventry to the Bonneville Salt Flats to test the first ever Bembo brakes on and XJR, and I bought with 18,000 miles on the clock with Jaguar Coventry , the first owner.
The car has been standing outdoors for 8 months, but when my Tesla went in for a new main batty (under warranty!), I drove it home.
OH dear only 17 miles, but it nearly conked out on me. I reckoned it was stale petrol, so I drained the tank and put fresh petrol in . Still not good, so got a local specialist to sort it out. £1,500 and four days later, it seems the filler tank seal had perished and water had got into add to the stale petrol,
. Two new fuel pumps, filters complete clean out of rust, (fortunately th engine is not damaged), eight new plugs, and now it is a sweet as a bird, BUT
I get an illuminated warning "Check Rear Lights. All bulbs working but perhaps faulty switch.How long should that take to replace , please? It is difficult to access ,so they want another £200 ( about $270 US).

 

Fault is more like in security & locking module in trunk next to battery.

 

Accessing the security locking control module (SLCM) according to your post is not difficult at all. A 10mm socket, extension and ratchet are all that’s needed. It’s located under the fuse box in the trunk. However, maybe finding a replacement SLCM (if that’s the problem) might be more of a challenge. Me personally, if all the bulbs are working, I’d replace all the tail light bulbs with new ones because maybe one or more of them have excessive resistance and could be right on the threshold of excessive combined resistance when illuminated. Just an idea.

 

Good idea I'll try that first. With over 130k miles on the ****, a new engine at 92k miles, the bulbs have lasted well! Thanks!.

 

This!
I had an intermitted message for the last weeks, thought it was the battery going out.
However, upon inspection, the rear light filament was broken, but made its mass through the filament of the rear light (same bulb).
New light bulbs and voila!

If not, a lower voltage battery (several starting attempts?) might be the case.
The brake light message is the very first indication that a battery is not up to par.