Honda Civic Horn Upgrade: Fitting Aftermarket Twin Horns

Select a twin high/low horn set; the Stebel Magnum electromagnetic pair used here cost around £17.26 and shipped with brackets and a relay. Alongside the kit, collect a 20A inline fuse holder with fuse, a run of cable rated at 20A or more, a handful of blue push-on spade connectors, one blue piggyback terminal, and red fork terminals (three for earths, one for the battery, one for the trigger tap). Decide up front whether your chosen horn needs its own relay: a high-draw unit does, whereas a modest replacement can be wired directly (see tips).

Take out the plastic flaps beneath the bumper, each held by one screw and two studs on both sides. Undo the screw and stud securing each wheel-arch liner and unclip the liner from the wing far enough to work; you need not remove it completely. Under the bumper, remove two bolts and two studs, then the screw at the top behind the arch cover. The lower bolts sit deep inside the two access holes and are roughly 8 inches in; use a 10 mm (No.10) socket on an extension or a flexible driver. With the fixings out, gently release the bumper, which clips along the top edge. Fog lights do not need to be unbolted: once the bumper is lowered there is room to unplug them. If headlight washers are fitted, either detach the pipe and cap or rest the bumper on padding to avoid draining the reservoir.

Fix the relay high in the engine bay, ahead of the fuse box, so it stays accessible without dropping the bumper again in future. Wire the four terminals: run terminal 30 through the 20A inline fuse to the battery positive, but leave that battery connection until last. Link terminal 85 with a short lead to the earth point next to the battery. Feed a wire from terminal 87 down toward the first horn. Run a wire from terminal 86 down to the horn area, where it will later pick up the factory horn-button signal.

Unbolt the original horn on the right-hand side and keep its bracket to hold the new unit. Earth one horn terminal to the ground point just above and to the right. Using the piggyback terminal, join the wire from relay terminal 87 to the other horn terminal, then add a second wire to the same piggyback and route it across the front of the car toward the second horn position.

The left-hand horn sits behind a plastic panel; detach its mount and reuse it for the second new horn. Earth one terminal to the ground point above and to the left, and connect the other terminal to the crossover wire brought over from the first horn. Set both horns to the mounting angle specified in the horn instructions and tighten the fixings.

The factory horn plug has two sockets: a long thin one and a small square one. The square socket carries the trigger signal from the steering-wheel horn button, so it feeds the wire going to relay terminal 86. Push the spike of a fork terminal into the square socket for a firm connection and tape it so it cannot pull loose. The original connector that used to feed the second factory horn is no longer needed with this setup, so tape it off and leave it.

With everything else complete, connect the fused terminal 30 lead to the battery positive. Press the horn button; the ignition does not need to be on. Both horns should sound together. Once confirmed, secure any slack wiring with cable ties or tape so nothing chafes or hangs into moving parts.

Reverse the removal sequence to reinstall the bumper, taking care not to pinch the headlight washer pipe and reconnecting the fog lights if fitted. When seating each wheel-arch liner, make sure the black plastic strip along its lower front edge (about the bottom 6 inches) tucks behind the bumper; otherwise the arch will not sit flush. Note how it was arranged during removal so it goes back the same way.