GE cooktop burner (4) over 20 years old, power goes on, the heater elements heat up but only has two settings off or red hot. The controls are located on the range hood, dial settings of low med med high and high no matter the setting is besides "off" the elements glow red hot. (very high).
Where do I look?

FYI: now element will not get hot at all. I noticed that when I remove/ re-insert & wiggle the element it heats up but then goes cold again. I purchased a new receptacle and a new infinite control switch from appliance parts pro. Since the receptacle was easier and it appears power is supplied erratic to the element I installed a new receptacle first, and yes that solved the problem. Well so far. Upon searching the posts I did not all of these symptoms as being a burned out receptacle. ie always glowing red hot when turned on.
Thanks