These work; I highly recommend them. I use them in my 220. THEY ARE 9-12 volt ONLY. Check the dimensions carefully to make sure they will fit in your tail light assembly. You want the 4 watt ones. These bulbs will also maintain a constant brightness even if you are using a generator.

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&category=CAR&Page2Disp=%2Fspecs%2F115x-x3X1W.htm


Don't bother with the LED bulbs made with a bunch of 5mm LEDs; they will put out less light than an incandescent. Useless...

If you're into electronics you could build your own lamps to run on 6 or 12 volts for $30 - $45 using off the shelf components, less than that if you build
your own current regulators. It's fairly simple to build a lamp approaching the brightness of something found on an emergency vehicle that would fit into something the size of a 544 light assembly. 444 could be done, but it would be a bit more challenging.

Bill