searching the wiring diagram for Electrolux Oven SK 7104 Type K40U ?

You better start believing. It is possible and very common for 2, 3 or even all 4 simmerstats to fail. The ones they use now are useless and very unreliable. What you describe is a common symptom of a failed simmerstat. The heat stays on high. I am perplexed that you state you are an electrician but don't appear to understand how a simmerstat works. It does not adjust and change the voltage. It changes the heat by switching on & off. The lower the setting the longer it stays off and shorter time on & vice versa. Wiring must be ok if you are getting power to the element when you switch it on. Simple test is to put the simmerstat from the one good element in place of one faulty one. If that element now works properly then problem solved and go buy 3 new ones. Also, as Peccavi stated all 4 simmerstats will be wired the same (unless 1 is a dual temperature element) so compare the 4 switches and check that the wiring is all the same. You don't need wiring diagrams for that.

Lincoln Appliance NZ
April 2013

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

wiring diagrams are not available to the public and can't legally be shown on the internet without permission of electrolux.If you go to a nice electrolux main dealer they might print you one off

CK
April 2013