Shut off all controls on the Jenn-Air and wait for it to cool. Unplug the cooktop's power cord from the wall outlet. If you're working on a gas model, close the gas valve inside the cabinet or island below the Jenn-Air.
Pull the knob straight off the shaft of the switch to be replaced.
Loosen and remove the nut on the threaded base of the switch shaft, using the wrench.
Take out the screws under the Jenn-Air's front edge where the appliance is attached to the countertop. Remove the retainer plate under the screws.
Wear work gloves while pressing upward from the bottom of the Jenn-Air to raise the cooktop slightly. Grab the raised front edge and tip upward at an angle. Prop up the cooktop with the metal rod.
Remove the switch from beneath the cooktop by pulling the part gently from its mounting bracket.
Slip off the two wires connected to the flat blades under the switch. Make a note of where the wires connect.
Slide the shaft for the new switch into the hole from the underside of the Jenn-Air. Snap it into position in the mounting bracket below the cooktop.
Push the two wires onto the flat terminals for the new switch. Each wire has a slide-on clip to hold it on a terminal.
Remove the metal rod and lower the cooktop gently to the countertop.
Replace the retainer plate on the underside of the Jenn-Air and secure it with the screws removed in step 4.
Twist the nut onto the threads of the new switch shaft and tighten with the wrench.
Align the D-shaped opening on the back of the control knob with the shaft and push on the knob until it seats on the shaft.
Plug in the power cord and open the gas valve below the countrtop or island if you're repairing a gas model.