Answering a challenge from our honored admin; a new tid-bit we haven’t discussed before now.
This is a fog light from my Mark V.
On my Mark V, as for your lights, there is one example each, one with 534486 on vertical and one with 534486 in the hard to read edging. There are a couple of other small differences between the two lights.
Some Lucas products have a month/year date, but I have not found one on these lamps.
Hi Rob.
Could it be the lens only is 534486 and the lens and reflector, as in the parts book, was allocated 534496?
Now I can’t sleep lol
Hello all, Is the correct Mark IV fog lamp an FT58? I see the FT58-2 shown in Rob Reilly’s above illustration, and it looks correct, but it has the Lucas badge protruding on the top. Someone said the Austin Princess used the FT58-2 but I thought the Mark IV used something without the Lucas badge similar to the FT58. Is the FT58 not illustrated in this catalog because it is from 1951 and therefore it’s not a current model used then? I am trying to find a pair but I can’t pin down what the car actually used. Signed, Very Confused
The fog lamps fitted to MkIVs were FT58. They don’t have the Lucas crest on the top only on the central member. As on this car.
Peter
Love the ACE wheel discs, very cool car. 
Cheers!
Peter is right about the FT58 being correct for a MKIV. The FT58/2 wasn’t available until 1950 / 1951 as I understand. I actually like the FT58/2 because it has the enamel Lucas logo which matches the headlamp. I have a pair of each (not for sale😉)
Here is the FT58 top.
Tim
What happens to the spokes underneath the discs? Do they get dirty and corrode unless you undo the spinner and take the disc off to wash them? That would be a pain.
Tim
There is a backing plate on the other side of the spokes so they are protected from road dirt but rather than an issue of dirt is the issue of visibility. If you can’t see the spokes then you can’t tell if you have any breakages.
Peter
It does seem odd. Aesthetics winning over pragmatism? Wire wheels dreaming of becoming a steel disc wheel? Rather ironic that most MK2 owners remove the steel rims and fit wire wheels.
I know that many RR owners have the ACE wheel discs fitted. Perhaps it was RR envy? 
Tim
Timothy, Thanks for the comment about when you think the FT58/2 was introduced. Could that be the reason that the prior model FT58, as used on the Mark IV, is not in R. Reilly’s posting that shows the Lucas lamps in the 1951 Lucas Spare Parts Catalogue? However, it does seem that slightly older Lucas lamps would be in there. You make a good point that with the enameled Lucas crest it matches the main headlamps nicely.
I interpret the catalogues as showing the then-current offerings.
Here are a couple of pages from Lucas 400B 1939.
FT58 is not shown, but on pages 168/9 it says the 1938 SS Jaguar 2-1/2, 3-1/2 & 100 used FT58.
Maybe the other way round; I read somewhere that the Ace discs were preferred by people who couldn’t be bothered to clean all those spokes.
I would have thought that someone who could afford a nice car like a RR, Bentley, Jag might have had someone to ‘do’ that sort of cleaning for them! 
Hi Gary,
If you wait long enough what you are after becomes available. There is a pair for sale on eBay which are sound but need restoration.
https://www.ebay.com.au/itm/125182965547?mkevt=1&mkpid=0&emsid=e11021.m43.l3160&mkcid=7&ch=osgood&euid=7473fe81db44408a811882a9ea0535b5&bu=43056920136&ut=RU&osub=-1~1&crd=20220305031341&segname=11021&sojTags=ch%3Dch%2Cbu%3Dbu%2Cut%3Dut%2Cosub%3Dosub%2Ccrd%3Dcrd%2Csegname%3Dsegname%2Cchnl%3Dmkcid
Hello Tim,
I have found it is very hard to find one of these lamps and here is a pair. Also, I have been researching the restoration costs for headlamps and spot lamps. At the moment I am waiting for a price quote for a pair of reproduction FT58’s from the UK company seen below:
https://vintage-headlamp-restoration.co.uk/lucas-spot-lamps/
I am impressed at the quality of the restorations and the replicas this company makes. It is tempting to buy these originals you have found. At the moment I am trying to weigh the restoration and related costs versus buying a replica set from the above company. They have not replied with a price quote.
Thanks for the lead and I will report what I find this coming week.
It’s worth noting that the lenses described in the advert have clear glass whereas those used in the MkIV have fluted lenses to give a low but wide beam.
Peter
That’s quite true, Peter. I think that the lenses might be more available than the lamps. I wonder if they were fitted to other Lucas Fog Lamps and might be interchangeable? Rob Reilly will know.
Stay well. I have Covid. 
