The wiring diagram is in the 79 factory service manual. You can order them from Zip Products.
If the head lights come up but don't come on and the rest of the lights....front/rear side markers and tail lights work, then the first place to check is the head light switch. As "John Z" in the old part of this thread, the lights are protected by a thermal circuit breaker inside the switch.
Check for power to the switch then, then the light switch on and check for power out of the switch.
My guess is you have either a light swtich problem or a wiring problem between the switch and the lights.