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

The first thing I would check are the dash grounds. Repaints and rust wreak havoc with them. Try running a ground wire to a clean portion of the dash directly from the battery and see what happens with the lights. If they get bright you know the sockets etc are all ok if not ground to a socket if it then works you Know there is corrosion between the socket and the dash if not then it is likely the wiring on the positive side or corrosion in the sockets themselves. Hope this helps. Good luck. MIKE

Mike, still lovin his 57 t'bird after 53 years!

yes I have add a ground wire

I would expect 11 1/2 volts to be sufficient for a 12v light bulb.  Can you pull the bulb and socket out of the dash, run a jumper wire to ground, if necessary and observe the operation of the bulb?  If it is bright, then you know the bulb and socket is working correctly.  If it is dim, see how much voltage is at the socket to rule out problems there and test the bulb with known good wiring and a 12v power source.  If those check out good, then there must be something in the panel blocking the light, dust, dead insect, spider egg sack, etc.

A standard bulb should work fine.  You have to be careful with LEDs as they project light in a relatively narrow angle, directly in front whereas a bulb can illuminate, say 270 degrees, it depends on the design, but a much wider range.  As a result, LEDs don't always work well when used in places that were never designed for them.  And, of course if your problem has nothing to do with the electric portion of the lighting, then an LED will not do a thing.



Lawrenceville, GA

Had the same problem after I restored my 55 Crown.  Changed over to 12 volt and could not see speedometer in the dark.  All other guages and insturment lights were good.  Problem was that the lens was not in the right location at the bottom.  The light for the lens numerals actually shines up thru the plastic to light up the numerals. Took speedometer back apart, made sure I put lens in properly and it lit up just fine.  If you didn't take speedometer assembly apart, previous owner may have and put it together wrong.
Ben

Ben HessTulsa,OK

thanks for tip about glass will check that out in am
jim

I don't know if you are aware that the headlight switch has a "dimming" function,
turn it all the way to the left (iirc) and you will have no lights, turn it to the right and
they will get brighter.

.


South Australia

check lens this am Its installed correctly/ I think at this point I will order a new lens /maybe after 60 years something with the paint inside lens has went haywire
jim

yes I know/ turned all the way up I have 11 1/2v

You have to have assembly out of dash and top bezel and smoked dome removed to see if it is installed wrong.  When I put my new lens in, I got it out of position at the bottom.  The two small screws still went in okay and re-assembly was easy but bottom edge of lens was not in proper slot.  You can check lens with it out with a flashlight- shine it up into the plastic from the bottom and watch the numerals light up. I only replaced mine because it was cracked but both would light up with a light from below. 
Pretty sure that will be your problem.
Ben

Ben HessTulsa,OK