After my passenger side dim headlight stopped working recently, I went to r/r the halogen bulb in it and discovered that, although the driver’s side headlight unit was tight in place, for some reason I could press on one end of the lens of the passenger side unit and it would go inward 1"-1 1/2" or so. This movement would correspondingly cause the opposite end of the lens to swivel outward the same distance, and vice versa. I subsequently noticed that sometimes my parking light on that side would go out on its own - by pressing the lens in on one end or the other it would start working again (or sometimes with a sharp rap on the top of the fender above the lens). I guess once I must have performed that movement with a bit too much force and it silently shattered the main halogen bulb (didn’t know the bulb sits that close to the inside of the lens! ), knocking out of commission both the dim and bright lights on that side. So, ended up replacing the bulb again.
Any idea what is going on here, and how does that affect the functioning of the parking light in that unit? An easy fix, or will I have to source another headlight unit (which = $$$$ if I can even find a good used one).
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
2
What MY car are we talking about? The facelift with the remote headlight adjusters?
Not sure whether they have, like the X-300s and XJ40s, the two adjusting knobs behind each headlight unit for “up/down” and “left/right”. I don’t recall mention of them in the owner’s manual set, if so.
The 96 has them. Look for yellow plastic pieces that snap somewhere into the body under the hood, behind the lights. When I converted my headlights to quads, they were removed.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
8
So, is this the system we’re talking about? For sure the headlight is not supposed to teeter-totter, so something has gone awry. It is the first I’ve heard of such an issue, though, so you’ll probably be on your own on diagnosis.
Hmmmmm. Dang, wish I had known about that earlier, as it seems I am always trying to rotate the halogen bulbs to aim the headlights properly (I think it was you, Kirby, who remarked in your book - or quoted another JLer in it - that the relatively dim cube headlights on the XJS “suggest light in front of the vehicle” or some such ) . Thanks for the info., VK.
This movement would correspondingly cause the opposite end of the lens to swivel outward the same distance, and vice versa. I subsequently noticed that sometimes my parking light on that side would go out on its own - by pressing the lens in on one end or the other it would start working again (or sometimes with a sharp rap on the top of the fender above the lens). I guess once I must have performed that movement with a bit too much force and it silently shattered the main halogen bulb (didn’t know the bulb sits that close to the inside of the lens! 
), knocking out of commission both the dim and bright lights on that side. So, ended up replacing the bulb again. 
) . Thanks for the info., VK. 