Why doesn't my sync cable work?
Make sure you are using RJ12 and not RJ11 ends. (The difference being 6 brass tabs instead of 4) RJ11's are physically the same size as RJ12's but will not work.
pin 1 --- white / orange (GPS sync)
pin 2 --- white / green (Serial Tx 9600)
pin 3 --- white / blue (Serial Rx 9600)
pin 4 --- green (Default Jumper)
pin 5 --- blue (Audio /GPS Power sync)
pin 6 --- orange (Ground)
(4th pair not used)