SAME EXACT thing happened to me when I first had my sustainer in- 1- what bridge pup are you using
2- rotate the bridge pup 180 degrees- I when that was done the sustainer harmonic mode worked PERFECTLY... Try it
Good old evil bay
but it didnt work so my tech took it apart and fitted the casing to a new black single coil driver...
but i do still have an issue with it so if anyone out there has a sustainer i have a question.
It sustains great in standard mode but as soon as you flick the switch to harmonic mode it stops sustaining...
ive tried all the standard bits
adjusted trim pots
any ideas ?