No headlights on '75 duster

Hi all,
I am having an issue with my Duster, and I need to display my embarrassingly green knowledge of electrical systems.
Basically the headlights are not working, and I don't know why.
All the other lights seem fine, blinkers, etc. I just replaced the headlight switch a few months ago, so i dont think that is an issue.
Browsing around, people say "check the grounds" etc, and i have no idea what this means or where to look. I took a headlight out, turned the lights switch on, and plugged in my voltmeter into the 3 connectors in various formation, but nothing "happened" on the voltmeter. I plugged in a new headlight for good measure, but no go. I checked voltage at the high beam switch and the voltmeter read 12V. Nothing noticeable is unplugged anywhere.
Could anyone give me some idea of what to look for here? In layman's terms would be ideal, i apologize for my lack of any electrical knowledge here. I am willing to take a crash course tho, because I need to fix this.
Thanks!!