What have I done

Without knowing what all you tore apart, hard to say. How do you know you got the signal switch together correctly, as that seems to be the central issue?

Start by disconnecting the flasher so you can troubleshoot it, and disconnect the battery. Get yourself a continuity tester.

The "truth table" for the signal switch goes something like this:

1 Make sure the 4 way flasher, if present, is OFF, or disconnect the switch/ flasher to be SURE

2. With the switch centered, the cold side of the brake light switch should show continuity to both rear lights only

With the switch to left, cold side of brake light switch should ONLY go to RIGHT REAR

Flasher "output" should show continuity to both front and rear left.

Opposite is true for right signal.

Unhook rear harness and see if that changes the problem, you may have a harness crossed or miswired

Best way to troubleshoot without risk of burning stuff up is to get a BIG test lamp---such as a spare/ junk stop/ tail light that you can wire up with clips, etc

Tape off socket so it does not short, and hook one clip lead to socket, other clip to stop filament.

Now hook one end of this mess to battery, but leave battery unhooked from car for safety, IE unhook battery positive clamp.

Now when you ground the test lamp it will light

Unhook signal switch, and hook the "ground" side of your lamp to each of the leads to the signal harness. You should be able to refer to the diagram and confirm that tan, green, etc, lights up left front, left rear, whatever, so make sure those are as they should be.