I have a 72' model and my dash lights only come on with the Panel/Dome switch is in the second or third position. Have you tested the switch or the bulbs? Otherwise your printed circut is not making a contact with one of the sockets. I think if one socket in the line is missing or the printed circuit is torn on the end they all go out.
My windsheild wipers dont work at all. I have found that the switch mounted fuse was bad (6amp) and the direction change contact was melted. I dont know exactly how the 74's are but they changed the switches every year. So It could be the switch or in the motor.
I hope this helps, or you already know all this. Good luck. If you find the problem let me know.