You might also explore the wiring scheme of the heating plate that is working - draw it on a piece of paper and then you'll have 25% of a circuit diagram.
Then you could replicate this arrangement on the other three plates.
The manufacturer would be foolish to let circuit diagrams escape - to do so would open them up to all sorts of legal action as frustrated users killed themselves one by one.
Good luck...
Peccavi
April 2013