When I installed relays and Cibie headlamps in my cars, I used 10 gauge wire. That’s probably larger than I need since I’m using only 60/55 watt H4 bulbs and 55 watt H1 bulbs, but it can’t hurt.
I couldn’t find any good sockets locally that use 10 gauge wire. Most of the connectors were phenolic resin that used 16 gauge wire. I’d read about ceramic sockets for headlamps on the Internets but never looked for them in earnest. When I broke a soldered wired off of one my headlamp sockets while troubleshooting a non-working turn signal, I thought I should find a socket compatible with the rest of the robust wiring.
I found these ceramic sockets on eBay and bought four of them.
They’re OK quality. The cover, which has a plastic hinge, snaps closed after inserting the contacts. I had to trim the tabs that hold the cover closed with an X-Acto knife before it would close completely. I soldered the wire to the connectors before inserting them in the sockets. At least they worked with the 10 gauge wire.