harold balls wrote:
My car (99 cutless) has display lamps out. [...] I took it apart and
found four little lamps with a blue piece of plastic over the lamp,
soldered to a circuit board. Only one of the four lamps was working.

Sure, you can solder in some new lamps. I did this to an old car stereo
that had burned out lamps in the display. I was able to get suitable
replacements at Radio Shack, but with their ever-dwindling selection,
this may not be possible anymore.

How does the blue plastic work? Is it a flat sheet of plastic that the
lamp sits next to, or is it a "condom" over the bulb? If the latter,
you'll most likely need to transfer it from the old bulb to the new
bulb. It's easy to find new clear lamps, but difficult to find
replacement lamps with this already installed.

You might try a hobby shop. People like to put tiny lamps in doll
houses and model railroad layouts, so they may have something suitable.

You may be able to use a #18, #73, #37, #74, or #70 automotive lamp.
These are small-diameter wedge base lamps, where the lead wires are
folded against the flat glass base to make contacts. You can
*carefully* unfold the wires to get something you can solder to. The
bulb is probably about twice as long as what you have now, and the
diameter may be a little too much as well, but these are fairly easy to
obtain. The wattage ratings are #18 0.56 W, #73 1.12 W, #37 1.26 W,
#74 1.40 W, and #70 2.10 W. You probably want the smallest wattage you
can get, like a #18 or #73. If you can find a #85 lamp, it's the same
size, but is rated at 1.12 W at 28 V. Running it on 12 V should give
you around 0.25 W, so it may work. Probably the simplest thing to do is
to get a #74 lamp as they are easiest to find, then decide if it will
fit mechanically, then decide if it is too bright. If these lamps fit
mechanically, you might solder a resistor or diode in series with the
lamp to drop the voltage to the bulb a little to dim it.

If you can find a 6 V lamp that fits mechanically, you could buy four
and wire them as two strings of two lamps in series. This will require
a jumper wire that's not currently on the circuit board, but is pretty
easy to do.

You could also install LEDs instead of incandescent bulbs. LEDs only
need around 2 to 4 V, depending on what color they are, so you have to
install a resistor in series to drop the 12 V to something suitable for
the LED. (There are "12 V" LEDs that have the resistor already built
in, but I've only seen these in red and green, not blue yet). LEDs also
have a polarity; if you buy the most common type, the round base will
have a flat spot in it next to one of the leads, and that lead must go
to ground. If the current bulbs have condoms, you could just skip the
condoms with a blue LED. If the blue lens is part of the plastic that
the lamp sits next to, a blue LED might be a close enough blue to work,
or you might install a white LED.

Digi-Key and Mouser both carry Chicago Miniature lamps. If all you need
are a few lamps, Mouser's no-minimum-order terms might be better for
you. Look at page 30 of Mouser's current catalog (at their web site)
for the ones that are closest to what you probably need.

Matt Roberds