2004 Prius Horn Install

The install of aftermarket horns in an '04 Prius is extremely simple, unless you are installing monstrous horns. The pictures below should be all that is required for installing most aftermarket horns.

The horns I used are Fiamm HK-9s, a disc type horn very similar to the factory horns, but larger and much louder. To locate a local Fiamm dealer, go here. The HK-9s should generally cost less than $20 each, probably closer to $15. I got mine from JC Whitney for less than $13 each. If you order them from JC Whitney, Google for discount codes, they are constantly running discounts, though lately many have had a minimum order size of $75 or so.

Click on the pics if you want to see the fullsize versions.

    Start by removing the fastening pins circled here...

    ...and here. Sometimes these pins can be a pain to remove. The trick is to use a Philips screwdriver, and just rest it on the cross on the pin, not putting any pressure on it. Spin the screwdriver until you see the center of the pin lift up a little, then hook a fingernail or small flatblade screwdriver under the pin center, remove the Philips screwdriver, and lift up on the pin.

    Once all the pins are out, simply lift the black trim panel up and set it aside. Directly under the hood latch, you will see the easiest horn to replace (aftermarket horn already installed). Simply remove the circled bolt, while holding on to the horn, and lift it up through the latch opening, then disconnect the single wire attached to it.

    If your aftermarket horn is like most, it can be set up for either 1 or 2-wire installations. If so, simply use the ground wire that should have been included with it, remove the horn from its mounting bracket if already bolted to it, and bolt the harness between the horn and mounting bracket. Then plug the wire into one of the horn terminals (check the install directions to see if it matters which terminal to plug it into - on most horns it doesn't matter, but it might on some).

    Plug the factory wire into the other terminal of the new horn, manuever it into place, and bolt it down. One down, one to go.

    The other horn is not so fun to work with. It is over near the passenger headlight, and you can barely see the mounting bracket and bolt, shown here. I can't quite remember how I managed to get it out of there without removing any more body parts, but it was possible. If you don't want to remove any more fasteners, remove this bolt, trying to hold on to the horn from inside the nose. If you don't mind spending a few seconds more to make it much easier to work with, especially if you are adding horns that have trumpets, read on.

    You only need to remove 2 fasteners in front of the horn to make it very easy to access it. The circle on the left is for a push-pin style, simply lever the center of the pin up with a flatblade screwdriver, and pull the pin out. The circle on the right is for a hood bumper, just use a Philips screwdriver to remove it.

    Once the 2 fasteners are out, simply grab the grille and pull forward as much as needed to access the horn. I personally would not yank the heck out of it, but as you can see, you can flex it quite a bit without hurting anything (the paint on the bumper has a flex additive).

    If the horn you are using is too large to fit in the stock passenger side area, you might be able to bolt it through the hole in the latch support behind the center horn, as circled, placing the horn on the passenger side of the latch support. Or you can replace the bolt for the center horn with one 15-25mm longer, and use the extra threads sticking through the threaded insert to mount a horn on the passenger side of the latch support, using a lockwasher/nut combo (or Nyloc nut). If you do this, you will need to make an extension wire for the factory passenger wire, just use a standard insulated male blade terminal on one end and an insulated female blade terminal on the other. It wouldn't hurt to wrap the connection to the factory harness with heatshrink tubing or electrical tape once you have plugged the extension wire into it.

    If you have some really large horns to install, it might be easier to remove the lower grille to work them into place. This is the graphic from the shop manual for the foglight grille, showing the mounting tabs.

    This is the graphic from the shop manual for the main grille, showing the mounting tabs.

    Start with the driver's side foglight grille (or grille blockoff plate if you don't have foglights). Pictured is the lower left mounting tab.

    I stuck my finger through the second from bottom slot to lift up on the tab. If you have smaller hands, you might be able to pull it from the bottom slot. Lift the tab up, and pull the foglight grille forward.

    You can try a finger with the upper left tab, but it didn't work for me, so I covered a screwdriver with tape as noted in the Shop Manual. NOTE - it is best to use at least 2 layers of tape. Press the small screwdriver between the tab and bumper, and wiggle it around until you can pull the grille forward.

    Another view of the screwdriver placement.

    The left tabs released. If you pull outward on the foglight grille, you should be able to pop the top right tab free pretty easily.

    The bottom right tab is a bit tougher, to avoid breaking the grille, grab it here and wiggle it around.

    The foglight grille out, you can see all 4 tabs. Repeat for the other side.

    Top right tab of the center grille shown.

    Wedge the screwdriver between the nose and grille, wiggle it around, and push the grille inwards towards the radiator.

    The tab released.

    Repeat for all the top tabs.

    The bottom tabs are tough to locate. Even in daylight, you may need a flashlight to properly highlight them. Again, insert the screwdriver between the nose and grille, wiggle it around, and push the grille towards the radiator until the tab pops free.

    Once all the tabs are free, push the grille into the opening. You might have to move it around a bit to get it past the edge of the nose opening.

    Rotate the grille face down to pull it out.

    Here you can see the bottom tabs on the grille, at the bottom of the picture. This is why the grille has to be pushed into the nose, not pulled out of it.

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Last modified: July 8, 2004
Copyright 2004, Tom Stangl