This posting is about completing a trouble-free Stebel installation in an Exige by using a relay and the least amount of new wiring as possible. There are many Stebel postings with lots of pictures, but those postings do not provide solutions to a quirk that seems to affect Exiges when routing new wiring across the scuttle area in the installation.
A couple of Exige owners (Doghouse and I) have experienced engine cut-out when honking the horn after installing a Stebel using a relay and (+) and (-) wires connected the Stebel to the Exige remote battery terminals. It seems the that certain wiring set-ups can cause electrical interference in the scuttle area beneath the service panels, which leads to engine cut-out.
Credit goes to Doghouse and TheViper for helping out. I am not an electrical expert, but I solved the cut-out issue because of their tips and by using a process of elimination to isolate the problem.
There have been many discussions about not needing to use a relay (see other Stebel posts), but the purpose of this post is to address using a relay in an Exige installation. Sourcing power for the relay in an Elise is a PITA, whereas it is a no-brainer in an Exige because of the remote battery posts in the scuttle area under the driver's service panel.
In this wiring, the OEM horn wires are used to activate the relay mechanism, and the Stebel uses 12 gauge power and ground wires. This wiring set-up will prevent horn wiring damage or possibly fire from the horn wires overheating, because the Stebel draws a lot more amperage than the OEM horn circuit is designed for.
- To remove the horn, use a small flathead screw driver to pry off the OEM horn connectors through the access holes in the CF. crash structure. Then pull and twist (C/W) the horn off. Use a magnetic thingie to retrieve the nut and lock washer.
- After removing the stock horn, plug the three holes in the CF crash structure using two 7/8 inch and one 5/16 black nylon hole plugs. This will help keep water out of the horn area when driving in the rain. See picture below.
- The OEM horn's positive wire (purple and brown) is attached to relay terminal 86, which I wired as the (+) side of the relay coil circuit. I made a wire extension to reach the Stebel.
- The OEM horn's ground wire (brown) is attached to relay terminal 85, which I wired as the (-) side of the relay coil circuit. Again, I made a wire extension to reach the Stebel and wrapped both (+) and (-) wires in wire / cable cover. See picture below.
- The Stebel's (+) terminal is wired to the Exige's (+) remote battery terminal using 12 gauge wire and a 20 amp fuse just before the terminal connection. This power wire is in a plastic cable cover that is routed through the radiator hose opening in the passenger side wheel well, up and across the scuttle area toward the driver's side, behind the brake booster and up to the (+) battery terminal. Route it around (away from) the main wiring harness. See picture below.
- The Stebel's (-) terminal is grounded to the chassis using 12 gauge wire fastened to the chassis (with a stainless steel fastener) using an existing fabrication hole drilled by the factory. This ground wire is about 8 inches long. See picture below.
Pressing the horn button cause the relay coil circuit at terminals 85 and 86 to close thereby bridging terminals 30 and 87 and sending power to the horn.
I was hell bent on being able to lay on the Stebel for as long as necessary, without electrical consequences, should the need ever arise. In 1996, I was at a stop-light in my new daily driver, and a jacked-up 4-wheel drive SUV ahead of me decided to change lanes and slowly backed into my car, over the bumper, onto the hood, and stopped when his tow bar was a foot away from my windshield. I was on the horn the whole time (about 10 seconds). The guy was apparently brain dead after a long day and said that he did not see my car behind him or hear its horn.
This scenario could easily happen in a Lotus.
Oh...this horn is LOUD