While installing some things I found convenient spots on the fuse block to access 12V power, switched 12V, and accessory power, so I thought I'd pass the info on.
These apply to the upper of the two slots:
B2-1: Switched power protected by fuse F60.
Normal disclaimer: This applies to my 2004 Volvo VNL780. Your truck may vary.
Update: A few days later I flipped over the fuse panel cover to find this information was already there on the legend. So much for my find...