Odd brake/tail light problem

Okay - got back to the car today with a clear head.

Changed out both tail/stop bulbs with new ones that are confirmed working. I tested the old ones and, for some reason, both bulbs' tail light filaments did not work. They were new. What's going on there?

I ran jumper wires from both tail/stop light housings to the ground by the trunk striker, which also has an extra 12 gauge ground wire back to the negative pole of the battery. There is lots of extra grounding back there.

I made up a wire and ran 12v from a keyed source (where radio was, I think) and tried each of the following three blades on rear light harness, one at a time:

1) Tail lights = came on (normal, not-too-bright)
2) right stop light = came on (bright)
3) left stop light = came on (bright)

Now... after I plugged the wiring harness back together, the tail lights are working (and I was right, it WAS the brake light filament coming on before) and the turn signals are working, sort of: the turn signals flash at increasingly slower rate if I turn on the parking lights (slower) or the headlights (slower still).

Brake lights still don't come on from brake switch application.

So I tried a different brake light switch. I mounted it on the door frame and grounded it, then plugged it into the wires coming out of the dash. Nothing. I switched the wires and still nothing.

Working my way back one step, I put the multimeter on each of the disconnected wires that connect to the brake light switch. No voltage to either of them.

Thoughts?