Do the lights go dim or do they actually go out? If they dim I'd say a bad ground/short, recheck your wiring or if they go out I would check the headlight switch.
Check the obvious first its usually there.
I'm sure that you can check the switch with a volt-ohm meter but I cannot remember the circuitry. Haynes and Chiltons can help you there. But if your not comfortable troubleshooting I would check that switch against a new one which I think there still available in the parts houses like Advance Auto etc.. If not the aftermarket does sell them. After all with that new wiring it would'nt hurt to replace the headlight and wiper switches.
I also had a bad dimmer switch go out and I had the same issue with my park light's.
Just a thought. Give it some time others will help also.
Owning nothing older- for long- a 68' I would have thought this would be the set up for all years from 65' but now I learned something new today. I guess 68 would be the most likely year for the change mainly due to all the mandatory safety improvements like those side markers and collapsable steering shafts, hidden wipers etc....