I have a 55 fairlane that I switch over to a 12 volt system and replace all the  6v  dash blubs with 12v 57 blubs also replace the 60 year old switch with a new 12v switch At night the speedometer lighting is so bad that you can't tell how fast your going/ I have 12 1/2 volts on the input to switch and 11 1/2 volts  out to blubs when knob is turn up as after as it will go Has anyone had the same problem? I'm think about replacing the 57 with led blubs,but not sure which one's will work the best If someone has had the same problem and went to led's and it helped  let me know which led's you used
ps
not sure if it work when car was a 6  volt car all the blubs were gone when I got it
jim