Bjorn - you and I seem to have the same vision problem.
The '69 is different from the '67-'68! The ignition lock was moved to the column in '69 and the back-drive linkage is used not only to lock the transmission, but also to turn the back-up lights on and off. In '67-'68 the switch was still mounted on the shifter somewhere, as Salmon wrote.
My thought is that if the neutral safety switch still works, i.e. the car con not be started in gear, then the back-up light circuit probably has a fuse or wiring issue, rather than a switch problem. Just my humble opinion.
Also, you don't need to have a switch under the dash if your linkage is disconnected. Just rotate the outer tube of the column about 5 degrees clockwise, and your back-up lights should come on. Don't forget to rotate it back, though! The key won't come out. If it does, the steering wheel won't be locked.
