What are you using to determine you have power to both sides of the brake switch, a test light or multimeter or something else? Just wondering what we're dealing with for tools. Can you post a picture of your column connector that shows the wire colors going into it? On the stock wiring it would have been a crescent shaped plug. Not sure what you might have for American auto wire. These are the wire colors for stock wiring, on the left is the under dash wiring harness side of the connector, the right is the turn signal switch wires that go up inside the steering column.
Colors of the under dash wiring harness side and what they are for.
black - horn button
light blue - left front turn signal light and left dash light
dark blue - right front turn signal light and right dash light
brown - power from hazard flasher
purple - power from turn signal flasher
yellow - left rear turn signal/brake light
green - right rear turn signal/brake light
white - brake light power when brake pedal pressed