'79 308 headlight ground location

I've been having intermittent problems with my headlights. Sometimes I will lose the left side light or the right side light, sometimes it is both the main beam and low beam, other times just one of the beams. When the lights are operational they are bright. I installed an auxillary harness a few years ago so that the bulbs are powered right off the battery through relays with the factory wiring providing the switching current to the relays. I bypassed the auxillary wiring and the problem has persisted. The fuses are good. I pulled the steering wheel multi-switch and cleaned the contacts with a liquid contact cleaner. The switch looks good to me. I'm challenged by electrical problems, but I suspect the headlight ground(s), which I have never cleaned. A wire runs from each headlight into the loom and disappears.....

Where are the headlights grounded to the chassis? Any other thoughts?
Thanks!