Philip -

Relax a look at the wiring schematic for the column signal wiring. The Full time B+ current goes into the brake switch on the orange wire and when the pedal is pressed, it makes the switch pass the current to the white wire that goes into the column signal switch. The switch then distributes the current to the Left and right wires that go to the back stop/signal lights. The left and right wires are Yellow and Dark Green.

So with the brake pedal pressed down check these wires for current at the column or the connector at the firewall for juice.

I just fixed one today where the connector terminals were corroded and the current couldn't pass from the column wire to the harness connector.

Joe