I use Clymer service manuals as a back up just in case I cannot get a Factory manual.
I prefer to use Factory Service & Parts Manuals for any type of work on a bike. Better photos and better directions in the factory manuals.
I think you'll find the majority will confirm the Factory manuals are the best way to go. I've had Clymer and Haynes manuals and they always seem to leave me needing more info.
Where can I go online to find the factory manuals? I need that should seem simple, but I did a search and it didn't yield anything.
Zanotti and Chicago HD are two of the lowest priced, best stocked on line dealers. Go to their website and search for the manual you want. You can find some on ebay also.