oven 220 wiring problem/oven support problem

[uncle al]

I am installing a new Kitchenaid combination wall oven and microwave in a new standard built in wall oven cabinet. The installation instructions are pretty straightforward, but when looking at the existing 220v wiring coming out of the wall, which my old Jenn Air oven was hooked up to, I have 3 black wires!! The new instructions show the expected red, white and black wires from thr oven to be hooked up as you would expect. I was unable to see during demolition which wires from the old oven hooked to which of the 3 black wires are coming out from the wall. How do I find out which of the 3 black wires hook up to the oven red, black and white wires?

Also, there is no instruction in the installation guide to show making or usng some sort of shelf or support arrangement for the oven to carry the weight. It seems that you just cut the opening to the correct size, slide in the oven, and secure it to the cabinet face frames with four screws. That just seems way to flimsy to me, but maybe is normal?

Any help/advice would be appreciated!!

Thanks

Alan

[LJR]

Al, you can find the wires you want with the use of a voltmeter or an ohmmeter. With the power off use an ohmmeter to see which wire has continuity to ground, that's your "white" wire. Or, with power on use the voltmeter to determine between which two wires you measure 240 volts. The "white" wire should be marked to identify it in some manner. No need to worry about red and black in this case, they will be interchangable.