I have not seen wirng diagram for the 68 radio.
There is not one in Ford 68 service manual.
They list the radio as using the same fuse (14A) that turn signals, back-up lights and windshiel washer use.
As I recall there was a one wire 12v plug in the harness near the radio, and a two wire plug from radio to speaker in dash.
Also an antenna lead from left front fender.