Hi Claude,
I couldn't find the wiring diagram for this model. There should be one inside the unit though.
Both oven elements should be bright red all around. Check it out. Set the oven to BAKE (350 degrees), give it a couple of minutes, then look at the bake element. If the element coil is not consistently red all the way around and has dark spots on it, the element is too weak and needs to be replaced. If the element looks to be ok, then check your oven temperature using an
oven thermometer.
As far as the top elements... Since you're saying that both elements do get hot, the problem is most likely with the switches. I know, it is unlikely for both switches to go out at the same time, but this is an older oven and maybe one of the switches started going sometime before the other did. If one of the elements weren't getting red hot, then I'd tell you to check both the element and its receptacle, but that's not the case here.
Hope this helps.