Pretty sure you need a Lucas MT211, like the repro one seen here: https://feked.com/shop/index.php?productID=551
Triumph used this lamp until the early 1950s, and the small lens MT211 would be appropriate for your 1947 T100. The repro lights also have provision for running a brake light.
Replica Lucas lights are also available from folks such as Domiracer.
Hope that helps.
That is the nature of my dilemma. I don't know if the 110 or the 211 is correct. Maybe Domiracer knows for sure. I may ask them.
I have a MT-110 replica but it is strange. It has two wires, One for the brake and one for the tail lamp. The problem is, there is now ground connection. The base of the of the bulb socket is pressure fitted into a large rubber washer in the base. There is no contact between the bulb socket base and the tail lamp mount.
I think I did solder a ground when I used a repop one on my 39 T100 but on the 48 T100 the repop had a 3 wire. Looking at the MT211 on ebay it has 3 wires and maybe thats the differnce as the original T110 were only two wires.
I think I'v figured it out. You do have to have an MT211 and you cant just solder a ground to an MT110. The sockets are different, the 211 has offset fixing pins for the double filament bulbs and the 110 has opposing fixing pins for the single filament bulbs.
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