Make blades by cutting 5mm x 20mm copper, .025' thick, bend 2 'right' angles by fitting into a slot in a piece of sheet steel & bending. _/-----. Solder wires to blades. Cross blade is"+", in-line blade is "-'. Assemble with small bolt or screw. rivet...

Also see CAT standard 12 VDC sockets, mounting plates, etc.

Connector AT (CAT) plugs & sockets are based on pins & spacing of AT automotive fuses, with the "+' pin turned sideways. The "12 VDC" is nominal battery voltage. Solar house wiring, RV, boat, etc.

Note: The AT size sockets the pins go into are Pico .205" x .025" female crimp sockets. If metal thicker than .025" is used (eg, .030"), the receptacle sockets will bend a bit and .025" plugs will become a loose fit. If you have the wrong thickness sheet metal for pins (eg, brass, copper or nickel-brass [AKA nickel-silver, german silver]) and a micrometer, you can pound it thinner with a hammer. (Personally, I'd have gone a little farther to make the sockets a little more forgiving,)