Hi Stuart, Dave, Scott and any others I may have missed,
I am the mystery man and owner of the Westfield SEiGHT with the high level brake light in question!
I travelled down to Gaydon with Nic Chase, AO from the Shropshire and Mid Wales Branch.
The brake light is an original Lucas item as fitted to the Jaguar XJS convertible which I purchased from a company called Fletchers in Birmingham who used to buy up large quantities of redundant Lucas and other British spares stock. Sadly nowadays they only sell new stock and have become very much your average type of motor spares shop.
I guess you could try some Jaguar/ XJS spares specialists or even breakers.
Than you for your kind comments regarding my car; so for information I built my Wesfield SEiGHT and put it through IVA in December 2010 and it has been on the road ever since; I use it through Autumn and Winter but not in snow!
The engine is a 3.9 EFI with 4 Litre cross-bolted block which was built from all new parts by John Eales; it has a finely balanced crank, lightened flywheel, fast road cams and the inlet and exhaust ports have been opened up. It produces 246 bhp @ 5845 rpm and 242 lb.ft of torque @ 4800 rpm and the power is very useable although you have to be aware of the torque when accelerating hard out of the tighter corners! But I can at least take roundabouts on in 5th gear if I am feeling lazy!!
I built my first Westfield 15 years ago with an XR2 engine with Webber DCEO 40 carbs and sold it to back Westfield after three and a half years before ordering the V8 kit.
Sorry I cannot help further with the brake light but at least now you know it's origin.
Best regards to all,
Malcolm Buttler.