Stu..ive got some brand new in the packet SP2 owners manuals I think - and they normally have wiring diagrams in the back I think. Let me know if your interested and ill have to go and dig them out.
Right..had a look and the manual says '851 SP '90. The picture of the bike inside has the earlier round mirrors which would point to the fact its an SP2 manual. Most of the info would be shared with the SP3 I guess..and it does have a wiring diagram in the back. I also have 2 copies if you both want one..£11 posted.