What's the best 12v switched power source.....

UN fused switched power comes from the key to the accessory buss in the fuse panel. So the fuse panel is "it."

If you want "run only" there is only ONE wire, so called IGN1 or "igntion run." It is also UNfused, goes to the cluster to supply the warning lights and gauge power, and branches off through the bulkhead to supply ignition, regulator, alternator field, etc

If you want to go to the trouble of splicing into the cluster power feed (hard to get to) and add an inline fuse of say, 5A or less, you could use that, which would then only power the gauges with key in "run"

Otherwise, any handy tab in the rear of the fuse box, on the switched buss, and put an inline fuse in that.

Lamp power is almost any orange wire from the dash lamp dimmer, IE radio connector