I have an old model Titzio 50, that after almost 40 years suddenly only glows faintly. I changed the bulb with original Osram H1 (12V 55W P14.5s) but got the same result. I chequed the old and new bulb with voltmeter and both are fine. The lamps shine bright when fed 12V directly. I measure no resistance between the rivets on the left and right leg of the lamp, but am not sure where I should find discontinuity for the two. There is no humming or visible flickering. The lamp was changed approximately 30 years ago from 220 to 110V (EU to US). I would like the lamp to shine bright again instead of the low glow, and would prefer to stay with my old lamp because the new versions are made from plastic instead of metal (really??). Any idea where I should start looking to identify the problem?

Theo Meuris, August 2019

OK, so the lamps shine bright when fed 12V directly.
Is the lamp actually feeding 12v in the first place?

There is a transformer in the base, I believe. If you can access that, you should be able to check if it is supplying 12v (probably AC).

Once you have eliminated the transformer it should be a simple matter to check the circuit from transfer to switch to lamp and back again.

If it is a high resistance joint and you are running a halogen bulb, it may be that the troublesome joint may run slightly warm with the lamp set "on" and at high power.

Hhfd, August 2019