I made this for a customer. He had a small Polaris ATV with a charge connector on it, but he didn't have a battery charger that would plug into it. He did have a battery tender with clips on it, though, so rather than buy a new charger just for this, I modeled this adapter in FreeCAD.

To assemble it, you'll need the connector to which you are adapting (obviously) with ~3mm wires attached as well as two each 1/4"-20 bolts (3/4" long), nuts and washers. Run the wires up through the two holes on the top half. Strip about an inch and a half and pull the wires down until the insulation is just below the surface. Make a hoop in the bare wire around the bolt hole. Lay the wires in the grooves and put the top and bottom halves together. Slide the positiveCap over the end that will be the positive side. For both sides, run a bolt through a washer, the wire hoop, the two halves and a nut - in that order - and tighten down, sandwiching the wire between the washer and the plastic.

There you go. Now you can clip to the adapter and plug it in.

NOTE: This should go without saying, but in today's world.... well, you just never know, do you? Anyway... Make sure that the positiveCap is printed in RED filament. Otherwise, it really doesn't serve any useful purpose, does it?

WARNING: Make sure you know which side is positive and that you wire this up accordingly. You have been forewarned so I will not be held responsible if you short something out; blow anything up; singe any hair; loose any eyeballs; electrocute any cute, cuddly bunny rabbits; rip any holes in the fabric of the universe; or any other unforeseen circumstances that may occur by the inappropriate use of this device.