
Horn Upgrade - DRAFT NOTES
last edited 21 April 2012
BMW Relay Part # 61.31.373.585
12V - 30A with resistor
Alternate Relay - VW/Audi Part #141.951.253B
12V - 40A with resistor
Although a single new horn with a higher decibal rating and power requirement may work without a relay in the system, it probably won’t work for long. The higher current requirements of the FIAMM or other similar horns will ultimately burn up the small contacts in the horn switch. As of this article, that’s $100.00/ list from a dealer for 61.31.1.244.420.
Disconnect Neagtive (–) battery cable prior to beginning any work on the electrical system of the motorcycle.
12ga wire, with an inline blade-style fuse, required from battery Positive (+) terminal to relay. FIAMM install instructions recommend 10A fuse with single horn installation. For twin horns, perhaps use 25A. For durability, suggest the weather-proof mini blade-style rather than a glass tube or euro ceramic fuse. NAPA part number 784667 - Mini fuse holder.
Relay Terminals and wire routing:
30 - 12V direct from battery to relay. Use 14ga wire, nothing smaller.
87 - Change over contact direct to horn terminal. 16ga wire.
85 - Extend original wire from horn (Green w/Black tracer) to this terminal. 16 ga wire.
86 - Extend original wire from horn (Brown w/White tracer) to this terminal. 16 ga wire.
A new wire is required from horn’s second terminal to ground. Ample grounds available near coil. Professional-grade electrical wiring, like coffee and divorces, begins with good grounds.
Space should be available to mount the horn relay just aft of and adjacent to the existing relays.
Solder, crimp, solder. Avoid the possiblity of future corrosion and degraded performance. Strip the wire end, twist and pre-solder the wire. Crimp the terminal in place using proper tools. Solder the crimped connection. Add shrink tubing to include covering the entire fitting on female blade connections. Use dielectric grease during assembly to insure long-term reliability of the junction.
Materials and Supplies:
One or two horns- Meyle, Fiamm, Freeway Blasters...
Relay- 12V30A with internal resistor (Resistors in relays supresses voltage spikes)
Quantity of male and female spade connectors for 14ga & 16ga wire
Shrink tubing, various diameters
In-line blade fuse holder and appropriate 20A blade fuse
Soldering supplies
Crimping tool
14ga and 16 ga wire (color to suit application)
Relays reduce the load, heat and wear generated on contacts and switches. Rather than forcing high amperage through a lightly constructed switch, use the existing switch to turn on & off a relay that can handle higher loads. Driving lights, horns, heated seats, hand grips and clothing are a few items that can benefit from the installation of a relay. If all these items were added, you would need to address your charging system capacity as well.
Horn relay installed adjacent others. Number '53" was on the VW/Audi relay I used.