D.I.Y. Hella Supertones Horn Install on 3rd Gen Prius Notes: I did not use the included Hella relay. I read the voltage on the factory horn signal wire and found it to be about 14.4 volts when activated. I’m not sure if the Supertones would be louder if I used the relay to a direct +positive source from the fuse box since they both returned the same voltage. If anyone has more info on this, please let me know. The Supertones are significantly louder than stock so I’m happy with the install even without the relay. Before getting started, you’ll need a 1” strip of aluminum to make a custom bracket as the stock Supertones bracket was too short to accommodate the larger horn in the factory location. I got a 1”x4’ strip at Lowe’s for $8. The bracket should be cut to 5.25” in length and mounting holes drilled to 5/16”. The original bracket on the Supertones needs to be removed and replaced with this. Use Loctite when attaching the new bracket as the original bolts holding the brackets on the Supertone were extremely tight. I fabbed up these brackets with a basic hand hack saw and a drill. Installation: Step 1: Loosen up the front bumper cover (sides and top only). There are two fasteners in each front wheel well as well as several clips and two 10mm bolts on the top part of the bumper cover. I didn’t remove the whole bumper. I just removed the fasteners from the top and front wheel wells and allowed the front bumper to pivot forward giving me sufficient access to do the install. Step 2: Remove factory horns. I believe each were held on with a 10mm or 12mm bolt. Step 3: Replace the Hella bracket with the custom 5.25” aluminum bracket if you have not already done so (see first picture). Ensure to use Loctite on the 13mm nut that holds the bracket to the horn. *disclaimer: Hella states warranty will be void if bracket is removed. Step 4: Install Supertones in the factory location. The factory horn signal wire fit directly onto the Supertones. I connected the factory wire to the copper colored Supertone connecter. Step 5: Make two ground wires at about 7” in length. Attach a female spade connector on one end and a ring connecter on the other. Connect female spade to Supertone and the ring connecter to the top radiator support bracket. This proved to be a sufficient ground. You can see the two ground wires attached with the yellow ring connectors in the following picture: Step 6: Test horn. Step 7: Reinstall bumper cover. Enjoy.