Shut off the gas line under the Frigidaire, turning the handle on the valve 90 degrees clockwise. Disconnect the electrical cord on the cooktop from the outlet below the island or kitchen counter.
Take out the bolts under the Frigidaire along the front edge where the appliance attahes to the underside of the countertop. Use a nut driver to remove these bolts, then slide off the retainer bar underneath. The bottom of the Frigidiare has sharp edges, so wear work gloves to protect your hands. Raise the cooktop at an angle from the top and support it with a wooden dowel.
Loosen the screw in the bracket holding the ceramic housing on the old electrode, which is tube-shaped, where it connects to the underside of the Frigidaire. Unplug the wire from the end of the electrode by pulling the metal connector on the end straight off the flat contact below the cooktop. Pull the old part out of the bracket and slide the new part in its place. Tighten the screw in the mounting bracket and slip the connector on the new electrode wire onto the contact.
Remove the support rod and lower the Frigidaire to its original position with both hands. Replace the retainer bar below the cooktop and secure it with the bolts and nut driver. Plug in the power cord for the appliance before turning the lever in the gas valve counterclockwise until the lever is parallel with the fuel line.