When working on these particular models (Highlander for 2005 and newer, Lexus for 2004 and newer), always verify and change fuses before starting your electrical test investigation. Pull the pad that connects the horn's electrical cable. Touch battery voltage to the horn terminal with a jumper wire to test the horn; if it doesn't work, replace it right away. When you depress the horn button, measure voltage at the terminal; replace the horn if you find voltage. Confirm the horn ground connection to the vehicle is properly attached and making contact. Start problem-solving by making sure power reaches the horn. When the relay tests good, check for power going to it in both control and power circuits. For each circuit without power, look carefully at the wires between the relay and the fuse box. Push the horn button with both relay circuits on and check from the relay to the button for electrical connection to ground; test this connection while looking for reasons why the circuit might not work (an open circuit) or find another issue if it works correctly. Press the horn button and see if it links to earth; if it does, look for a faulty connection between the relay and horn. You need to take out both horns from the location right in front of the windshield glass. Lift up the trim panel on the radiator support and unhook all the fasteners. Pull it away from the support and grille, and take it down. Unplug the connector to get rid of the horn connected to the fuse and relay box in front. After that, loosen the bracket bolt in the horn's mounting position. Before taking out the horns in front of the condenser, disconnect both their electrical connection and loosen the mounting bracket bolt. Unscrew the bracket bolt to take out the part, and putting it back in follows the path opposite to this removal.
