There is an additional 4 pins on a 24 pin mother board power connector when compared to the older 20 pin mother board power connector. Duh! The power connector is wired and keyed so that you can plug in a 20 pin power connector into a 24 pin and vise versa (although the additional 4 pins hang over).
Some new power supplies allow you to remove those additional 4 pins to keep them out of the way when using an older 20 pin motherboard. I never realized those additional 4 pins are keyed the same as the 4 pin auxiliary 12 volt plug that applies additional power to the CPU. It never even dawned on me to try to swap those.
This guy managed to stretch his add-on 4 pin connector to the 12 volt plug. One would think by all the extra work he had to do to stretch it far enough should have been a clue that maybe it doesn't go there.
In any case, this mother board was fried by the time we got it.
Although this isn't the kind of thing I would have thought to do, it does bother me slightly that they aren't keyed differently.