We are an early Home model which has one. Having just finally hooked it up to the speedometer, which was rebuilt, we noted that the light comes on at 22 mph. Wondered if that point could be adjusted to something like 30 or 35, because that would be useful to help keep from exceeding the local school zone speed limits of 25 mph. (The fine is at least $200, plus a large black mark on the driving record and increase in insurance costs.)
So now we will look for the adjustment control inside the speedometer.
The light does go out after increase from its starting point of about 10mph, and it stays out thereafter up to terminal velocity (when the front becomes airborne due to lift from the "wings").
As the speed decreases the light will come back on again until getting below the starting point.
If the speed is varying around the lower or upper points, then the light will blink.
All can be turned off by twisting the lamp.
Octagonally yours, BOXLEY (Robert and MGTC0820)
I have revisited your car details..particularly the Peter LLoyd dealer's plate.
In your photo these two plates are not attached in an original way (only two pins in body plate) and the Lloyd plate may even be from a different car.
The records list Lloyds having sold several TCs new in 1950 (they were not involved earlier)
The only one with a chassis number after 10,000 is TC10069 and the records are hand written and complete. I guess we will never know!