You can replace the entire taillight/front signal assembly,
or replace just the bulb.  Bavarian Auto sells them
(http://www.bavauto.com/lview.asp?imgfile=assets/imglib500/19263.jpg) or you
might be able to buy
them locally since they're PIAA.

FloydR

Hello BMW owners,

I have 1999 323i, with regular bulb-lamps for its lights (headlights,
signal, tail lights).  I know there is an option to replace the
headlight with halogen -- but I was wondering, I see that there are
LED lights to replace regular bulbs for flash lights and some lamps
for home.  Is there any similar products for cars?  I don't think LED
is bright enough to use for headlights, but I think it can be used for
signal lights and taillights as new cars used these days.

The replacement LED lights I mentioned for home lights have the same
screw for the socket but just with LEDs.  So new LED lights can be
used without buying whole new one.  I was hoping to find similar
products for tail/signal lights for my car.

Does anyone know such products?

Thanks.