Jenn-Air element won't shut off

Question

I have an older Jenn-Air model 2800 electrtic range. I have a grill cartridge on the left that I use twith the griddle. As of yesterday the element won't completly turn off when you set it to off. The top,longer element stays warm and the exhaust fan stays on low. I replaced it with a 4 prong dual cooktop cartridge and that works fine. Is it the 5 prong grill element, or the switch?
Thanks, Jimmy.