I believe you're correct, Drew. The 3-prong plug is two hots and a ground, and the 4-prong plug adds in the neutral. I'm no electrician though, but come stare at my panels any time..
82 fj40, 99 uzj100, 06 gx470
05 525EXC, 01 XT225, 09 TTR125, 07 TTR90, 07 CRF50