Author Topic: Horn circiut wiring layout  (Read 46 times)


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Horn circiut wiring layout
« on: 20 July 2020, 05:21 PM »
Another day another project.  I'm finally installing my air horns.  The dash switch is the MB SPDT fanfare switch to select between the regular horns and the air horns.

[sidebar comment:  as far as I've been able to learn, the idea of the switch is to select between the horns.  I wanted it to add the air horns on top of the regular ones.  However, oddities in the electrical system prevent this.  The usual horn relay circuit has an odd ground loop or something that prevents this.  If anybody has figured this out please step forward!]

Anyway, according the schematic, the respective original horns each have black/yellow/pink (auf Deutsch SW/GE/RS) wires leading back to the steering column combo switch where they join.  That is then run through the steering wheel horn momentary contact switch.  The normally-open side of the switch is connected to ground.  The hot horn leads feed back to fuse 8 in the fuse box.  Press the horn, the circuit is connected to ground and the horns sound.  My idea for the air horns is that the horn button goes to the middle of the SPDT selector for grounding-when-pushed while the other poles connect back to the original horn or the air horn relay. 

So, what I need to do is access those SW/GE/RS wires under the hood.  This may all sound like gobbledygook, so here's the bottom line:  Does anybody know where those horn SW/GE/RS wires pass through the firewall from the cabin to the engine bay?  I'm assuming that it's in the large bundle passing through the fuse box, but who knows?  I don't want to start hacking up the harness without assurance that both wires are there. 

I tried to post a schematic of all this but am having picture problems.  :-\

If this is too unclear pls lemme know.  Thanks in advance,
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0