Turn the onyx countertop upside down immediately after it is constructed, prior to installation over a cabinet. Measure the continuous flat onyx surface. Transfer the measurements to large craft paper. Cut out around sinks and stop prior to any joints.
Cut the paper to fit the underside of the countertop exactly. Note the location of the electrical box in relation to the anticipated installation of the counter. Send your template, measurements and floor plan directly to your electroluminescent light laminate manufacturer to have a custom light tape made for your counter.
Install an electrical box close to the installation location of the electroluminescent light laminate. Most electrical boxes nail to a close stud or support wall or wood block using a nail provided with the box and a hammer. Some manufacturers provide the electrical box and ballast unit as a package so that you will only need to route your house wiring into the electrical box at the openings provided. Do not connect your electrical leads until the unit is installed.
Attach the light tape to the underside of the onyx based on the electroluminescent light laminate manufacturer's recommendation. Use hook-and-loop tape or transparent foam tape to attach the light tape to the stone.
Install the electroluminescent light laminate lighting ballast inside the electrical box if it is a separate unit. Route the lighting tape conductive electrodes tail and connector tail through any walls or cabinets and into the electrical junction box for connection. Follow the manufacturers directions on connecting the tails to the regular house current. Some systems allow you to plug the tails into a plug receiver on the lighting ballast.