I've got some original Hella horns, original equipment on the car, but they've been silent for 30 odd years. Putting 12 volts across the lugs doesn't do anything.
Modern replacements look all shiny and new, even though it's something nobody else will likely ever see I thought I'd try to bring the originals back to life.

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Opening them up they actually look pretty good.

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I don't see any broken wires, and the corrosion is minimal. The sprung contact points on the right don't seem to be connected in a way that would allow the thing to move in response to the magnet.

Anybody know what I'm looking at here? Any particular diagnostics I can do?

Note: I've never played with one of these - hopefully others with direct experience will chime in.

Operational principle is of a simple electromagnet. Contacts are a make/break affair in response to the diaphram moving.

Check coil continuity with DMM. I would suspect contacts should be starting from a closed condition.

our man carson (ex navy seal) restores these horns here at our shop and gets the vast majority to work again is usually the points.

Ive done a fair # of them your example is a very early version since it has actual screws later ones used rivets.
Because of their location ...corrosion!!

I kept mine (both broken), put aside to tinker with at some later point. So tracking this thread with interest.

Anyone know what the original "factory-fresh" finish would have looked like?

- Tony

When you give it 12 volts, does anything move, even once?

What are you using for a power source? I haven't messed with my original horn, but when I hooked up my brand new Hella Sharptones to a 12v, 3 amp power supply, I got nothing. When I hooked them to a charged car battery, they about broke my eardrums. I just needed more current to get them moving. Not sure if that applies to the old horns.

I’m using a 10 amp battery charger. I get nothing when it’s connected.

Try a battery per @bbrock suggestion. Some battery chargers aren't true DC voltage output. There are some battery chargers that are simply half wave rectifiers and may not drive the electromagnet properly which is looking for a solid 12v DC.

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https://lastminuteengineers.com/the-half-wave-rectifier/

Use a car battery. Remove the potting from the adjustment screw and after its all cleaned & reassembled adjust to the correct tone...Just wear ear protection

Rich knows! My horns work and look factory new! THX