From web searches, apparently some MP3 taggers include cover art and other crazy tags, which can confuse the Ford car stereos. Maybe my FLAC-to-MP3 script pulled in some such tags (as it seemed to go to internet to pull tag data).
So here's a quick and dirty Ubuntu script to iterate over my entire MP3 collection and rip out any dicey looking tags.
strip_unwanted_id3_tags.sh
for TAG in TCOP APIC PRIV TXXX TCOP MCDI POPM TCON TDAT TENC TLEN TPUB TSSE WXXX do echo Stripping tag $TAG from all MP3 files below current folder... find . -name *.mp3 -exec id3v2 -r $TAG '{}' \; >/dev/null done
The list of tags to remove came by using 'id3v2' to examine the entire collection, removing the more rarely used tags plus the album art ones.
This seems to make my Ford Focus accept the 128GB FAT32 USB stick. In early testing however it has failed to play tracks in correct order - grrr....
By contrast a VW car stereo of a similar age (their RNS 315 unit) accepted the original unaltered MP3 files on a 128GB FAT32 SD card and just worked! Much more impressive...