I can’t speak for the SD card part of your question as I haven’t tried my Fuze in my car yet.
When you connect a Fuze to a computer though, the SD card shows up as a seperate disk. Perhaps the car’s stereo can’t deal with the way the Fuze offers access to the SD card. There are (cheap) USB stick shaped micro-SD card readers. Perhaps that would suit your purpose here. Just put the micro-SD card in the USB stick’s reader and put the USB stick in your car’s stereo.
USB thumb drives should work fine in car stereo’s with an USB port. I have tried several different USB memory drives and they all worked fine.
