Found what I was looking for Some sockets have built in resistors and use a 2.5 volt bulb, others have no resistor and use a 12 volt bulb. Be sure to get the correct bulb or else the light won t work
What it shows; fuel warning light TC/TD 2.5 volt British no. 970, US no 223 0r 233
12 Volt British no 986 or 987, US no. 1446
I do not have a catalog for the British, but for the US 223 is type FE-3 1/2, voltage 2.25, amp .25, average life 5 hours
For the 233 G-3 , voltage 2.33, amps .27, average life 10 hours.
For the 1446 G-3 , voltage 12, amp .20, average life 250 hours,
As a point of interest, it states that the 223 and 233 use in flashlights, and the l446 in toy trains. I would guess that the 233 and 223 were used because they had a lot of them.
I would take my recommendation, and use the 14.4 volt bulb, which is for auto, it will take the bouncing and other G forces better, and it will last longer, current is also a little less, will not be quite as bright, but will do the job.
Cheers Dean