Drew,
The photo below on the left shows the B-9294 clip used to retain the brake light switch wires to the left leg of the K-member and the photo in the center shows the hole in that leg where the clip is bolted to the leg (about half way along the bottom flange). From there it is routed immediately below the pedal bracket and then upward to the brake light switch on the transmission shift lever housing.
On the handful of super-early frames that have no legs on the center cross member, the wire just hung in the air between the light switch housing and the pedals before being routed upward to the brake light switch on the transmission shift lever housing. On very early frames with early K-member legs, there was no hole in the lower flange of the left leg for a B-9294, but likely a spring clip such as B-14585, shown in the photo on the right, was used to retain the wires.