Electric magnetism...It burns.

So I hooked up the third and final powerboard today.
Then I finished creating the third powercord mini-harness for the three extra solenoids.
Finally I turned the power on and tested the coils - first one ok, second one ok and we got smoke. Smoke?

Turns out something wasn't right with the third (actually first) MOSFET so it was in a always-on state.
This of course caused the magnet it was connected to to be always on, causing it to get EXTREMELY hot! I mean, surface of the sun hot.

And then I accidentally touched it, just to be sure it really was hot. It was.

Tomorrow's another day and then I'll troubleshoot the board to see what's wrong with it. Most probably I'll switch the faulty MOSFET and the accompanying resistor to make sure it works.
I really, really, really wish I'd tested the board before mounting the harness and the board etc...

Anyway -
Thinking the MOSFET is toast anyway, I decided to videotape its last moment on this planet doing what it should do - grabbing balls.

Edit....
Now that I think of it - the MOSFET is probably fine since it does in fact work. Maybe it's just the resistor that needs changing. Does anyone know if a broken MOSFET leads current...?