The later Magic Pies and Smart Pies with the Vector controller have the three wire brake cable but only use the Black and Blue wires for the standard mechanical switch:
The Hall sensor type
(as shown in your link) requires the additional +5V feed from the Red wire for the Hall sensor to work.
It should be possible to remove the cable and connector from the GM brake lever, and then solder it to the Hall sensor wires to allow it to plug into the Magic Pie's control Harness.
GM Canada sells the hydraulic brake systems with the Hall sensor integrated into the brake lever assembly:
They come already fitted with the correct connectors to plug straight into the GM control harness
(as shown in the top photo).
Alan
