Looks like a din socket https://www.furneauxriddall.com/acatalog/Hella-DIN-Plug-16A-8JA-002-262-003.html?gclid=CjwKCAjw1cX0BRBmEiwAy9tKHrQbxLvQWHE085m5YjQBNqO-oBgTnEKrZgJJq-8O0BisOuXc3MYyqxoCdzcQAvD_BwE