Air horn wiring advice...

The 70s population must have been half of what it is now and the economy much worse but many agree about the bridge bringing its own problems. Still it’s one of the best places in the world to live. But the battles go on ruining the place for the sake of tourism, locals priced out of housing because outsiders buy up property to let to tourists etc etc.

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Good stuff! What a clear diagram. I'll give my installation plan a rethink after seeing this relay with incorporated fuse and being able to operate either horn with the push on the indicator stalk... Thank you...

Ok this is very interesting but I really don't know much about circuitry so I have some dumb questions...

1: On the diagram, I don't understand what terminal 87a is connected to? All the other numbered terminals seem to be connected to a positive or negative wire but not 87a.. It looks like it gets a positive current via terminal 30 when the switch next to the letters "NC" connects. And when the switch opens, the positive current goes by "NO" to terminal 87 and onwards to the horns themselves. So 87a is a mystery to me...

2: I have a separate 30amp fuse on a heavy-guage cable which I shall be connecting between the battery positive and terminal 30, so I don't need a relay with a built-in fuse. But is the relay in the photo a 4-terminal relay or a 5-terminal relay? (Which leads me back to my confusion over terminal 87a....)

Sorry I'm being a bit thick but that terminal 87a is confusing me...

I am no electrical guru, in fact I know sweet fa about electrics, so please consider this when reading this reply.

I think 87 and 87a are an either/or connection - not both.
NC = normally closed
NO = normally open

You want to connect to the NO as the circuit then is normally open until you press the switch and it goes to closed, thus supplying power, and operates the horn.

If you connected to the NC, the circuit would be normally closed, thus supplying power, until you press the switch which opens the circuit thus cutting power to the horn.

I haven't really done much on the electrics side so I find this type of thing interesting!

Good luck with your project.

M

Thank you Herr Doktor Merkwuerdigliebe! That clarifies everything for me. So it's a standard four-pin relay, which is a relief... "Mein Fuehrer! I can Walk!" Best film ever....