Although Carl Allison’s wiring diagrams (on Gregory Bender’s site) are generally very good there are some discrepancies that I have found between them and Moto Guzzi workshop manual diagrams. Blue wires are sometimes shown brown, as in the feed to the T3 front brake light switch and brown wires are sometimes shown black as in the feed to the T3 horns. I have prepared my own drawings for these bikes with the errors I have spotted corrected, pdf copies are free to MGCGB members.
Edit - This is no longer the case as I had an unfortunate experience (see here) so I no longer give these out free of charge.
I think the errors have come about because the source material is in Italian and the colour names Nero = black, Marrone = brown and Azzurro = blue may have been unfamiliar. I have also noted differences on some of his other wiring diagrams where Bianco = white is confused with Marrone = brown. I cannot be sure that there are not any other errors and would suggest that you confirm any that you are not sure about with the Moto Guzzi workshop manual diagrams.
Good luck!