Going back to the fuse block that's the subject of this thread, I heard back from the good folks at Motolight, and they advised me that they never wrote an Installation Guide, but they gave me the info I needed over the phone.
So for the sake of anybody who might be wondering sometime in the future, and might stumble on this thread, the Motolight Power Fuse Block (#65229) has a capacity of 30 amps. There are three circuits, each has a max power rating of 10 amps. All three circuits are switched. The entire unit is controlled by a single relay.
There are three connections to the bike's wiring harness. Red goes to the +POS terminal on the battery, and this line should be protected with a 30-amp fuse somewhere between the battery and the fuse block. Black goes to ground, and can be grounded to the -NEG terminal on the battery or anywhere on the bike's frame where you can make a good strong connection. The third wire is yellow, it's the trigger wire, and it's located between the upper red wire and the lower black wire.
There are six spade terminals for connecting accessories to the power block--two terminals for each of the three circuits. These six terminals reside in the upper half of the block, above the fuses, or you could say they reside on the "red" half of the block. There are also six spade terminals on the lower half (the "black" half) -- these are all grounds.
In the picture below, the terminals are identified by the fuse they are connected to. To be clear, you can connect two accessories to each circuit as long as the total draw of the two lines doesn't exceed 10 amps, and you should choose a fuse for each circuit based on that total draw.