Check the TSRM, it will become your friend. Trust me. And I have the same problem, except when I try to turn mine over all the power cuts out.
It's either wiring or the starter.
If you are not on Supramania, I suggest joining over there as well, I find the members and posts to be more helpful over there.
TSRM:
MK3 TSRM On-Line
Hope this helps