Install The Stebel Nautilus Horn on a Lotus Exige and Elise

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The Lotus Exige and Elise are notoriously difficult for some drivers to notice due to their small size, the ever growing girth of U.S. vehicles, and distractions (e.g., smart phones). The OEM horn supplied by Lotus just is not loud enough to get the right amount of attention when needed. The Stebel changes that, if the Lotus horn is a 5 the Stebel is an 11.

These instructions will provide a guide how to upgrade the OEM Lotus horn to the Stebel Nautilus. Just one close call avoided by this upgrade pays for the entire thing.

  • Heat gun
  • 13mm wrench (a.k.a spanner)
  • Wire cutters, stripers, and crimpers
  • Drill and drill bits
  • 8mm socket and ratchet
  • M5-0.8x12mm bolt, nut, and washer

These instructions and required parts list assume the Stebel Nautilus purchased included the following items: Stebel Horn, 4 pin 30amp relay, Mounting bolt and nut

If the relay is missing any Bosch style 30amp 4pin relay can be purchased at an auto parts store. Buying one with a weather resistant housing and matching connector is recommended. This is completely optional and not covered in these instructions.

Remove the OEM Horn


Lift your Exige on jack stands or with a hydraulic lift.

Follow the instructions here to learn how to safely lift your Lotus Exige / Elise.


Remove the clam

If you're hands are small enough or your front oil coolers have been removed it may be possible to perform these procedures without removing the clam. These instructions are based upon having the clam removed.


Remove the under tray

Remove the 9 x 8mm bolts on the left, right, and rear sides (A,B,C) securing the bottom of the clam to the crash structure underneath the car.

Note: These instructions assume the clam has been removed although the picture displays it in place.


Remove the stock Lotus horn

  1. Remove the single bolt and nut securing the horn to the crash structure
  2. Disconnect the two wires attached to the horn.

Mount the Stebel


Determine where to mount the Stebel horn and relay.

Stebel horn

  • The horn must be located in a dry area not exposed to road debris and direct moisture. If moisture cannot be avoided ensure the horn is mounted at a minimum of a 90 degree angle from the direction of the incoming moisture (rain).
  • Front brake cooling solutions, if present, may result in the stock horn location being unusable due to the increased size of the Stebel. Once a location is found, if needed, use a drill and 5/16" bit to create a hole in the crash structure to push the bolt included with the horn through for mounting.
  • Install the horn, use Blue locktite on the threads, and tighten the nut down until the horn is securely mounted to the structure.


  • The relay can be placed anywhere; the closer to the horn the easier the install.
  • If mounting underneath near the OEM horn mount, keep in mind the radiator lines may need purged at some point. Leave room to pull the coolant hose off without the relay getting in the way or wet.
  • Use an M5 bolt, nut and washer to secure it after drilling or using an existing hole.

The image below depicts an excellent mounting option that supports brake cooling solutions and does not impede purging the coolant system. Three holes must be drilled to support this mounting location.


  • Consult your Stebel packaging to determine the max amperage draw as these instructions assume it is less than 20 amps.
  • Ensure the new wiring is capable of handling the amperage draw over the length of the power and ground wire.

Horn trigger

Locate the wires that were connected to the OEM horn. The positive wire is purple/yellow and the negative is brown (or really dark in color). If both wires appear black, use your finger nail or cleaning solution, such as WD40, to clean the wires.

Optionally - replace the OEM connectors on the horn wires with 22-18awg weather resistant female terminals. Use the Heat Gun to shrink the terminals generating a weather resistant seal.

Wire the purple/yellow wire (positive) to terminal 86 on the relay

Wire the other brown wire (ground) to terminal 85 on the relay

Depending upon the chosen mounting location for the relay the OEM cables may not reach. Use weather resistant butt connectors to extend the wires to the relay.

Image 7676 from Install the Stebel Nautilus horn on a Lotus Exige and Elise

Run 12v power to the Stebel

The Stebel requires more power than the OEM Lotus horn and therefore must have a dedicated line run to the 12v battery.

Install Fuse holder

  • Place your inline 20/30 amp fuse holder near the brake reservoir where it will be accessible by removing the accessory panel for future maintenance.
  • If the fuse holder wire cannot reach the positive charge terminal from the chosen location then cut a length of red 14ga wire long enough to connect the inline fuse holder to the Exige's positive charge terminal (to the right of the brake reservoir).
  • Install a Ring terminal large enough to fit over the positive post while being secured by the nut on one end of the wire.
  • Use a Butt connector to join the red 14ga wire to the wire on the inline fuse holder.
  • Use a heat gun to shrink the connectors making a weather resistant connection.

Run power to the relay

  • Cut a length of red 14ga wire long enough to reach from the inline fuse holder to the chosen mounting location of the relay.
  • Connect this wire to terminal 30 on the relay with a female quick disconnect terminal.

Protective wire split tubing

If desired this is a good time to install protective wire split tubing to encase the wires. This is completely optional.


Ground the Stebel to the chasis.

The Stebel horn negative terminal needs grounded to the chasis. Some cars have a machine screw already in the frame on the left side, others do not. If your's does not, get a machine screw and appropriate drill bit and create a hole in the aluminum frame near where the A-arm bolt is. The screw only needs to be big enough to hold the ring terminal, otherwise any size works just fine.

1) Cut a length of black 14ga wire and install a female terminal and ring terminal on the ends.

2) Find a location and drill a hole for the machine screw.

3) Place the ring terminal on the machine screw and screw into the frame until tight.


Wire the Stebel horn

Wire the Stebel positive terminal to terminal 87 on the relay

  • Cut a length of red 14ga wire long enough to connect from the relay to the positive post (A) on the Stebel horn.
  • Install female terminals on both ends of the wire.
  • Connect the wire to relay terminal 87 and the positive post on the Stebel horn.

Connect the ground wire female terminal to the negative post (B) on the Stebel


Test the horn!

  • Turn the ignition to accessory mode (the radio turns on).
  • Plug your ears
  • Hit the horn

Reference Section

Below are the Stebel instructions provided with the horn for reference. These explain how to retain both horns if desired.

Image 7705 from Install the Stebel Nautilus horn on a Lotus Exige and Elise

Congratulations you now have a superior horn to help avoid traffic incidents or just have fun with. Reinstall your clam, under tray, and accessory panels.

DISCLAIMER Last updated August 28, 2021

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