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As a new to me Locost owner I've had a number of challenges, but this one has been the most frustrating so far. I replaced an anemic (1/2 of a Ford dual horn system) with a Hella supertone copy. I was pleased to see that there was already a relay to the horn through the "Painless" type fuse block. I also added a decent push button on the dash. The horn sounds excellent when parked, but will not work with the ignition in the on position?! The relay supply wire stays "hot" with the ignition in both positions, and the horn button "hot" wire stays powered in both ignition switch positions. I have found that the non-hot switch wire is grounded with the key off, and "open" with the ignition switch on. What do I need to do or look for? Any help would be extremely appreciated! Thanks!

Here's some genuine Lucas horns https://www.bonhams.com/auctions/18295/lot/4/

Your ground leg to the switch has to go to ground with the key on for the horn to work.
It sounds like your power goes from the power block to one side of the relay and the common terminal on the switch.
Then one wire goes to the horn (from the N.O. terminal) and one goes to the switch (from the coil), the body of the horn is grounded along with the "other" side of the switch.
When you activate the switch it completes the circuit for the coil which turns on the relay, allowing power to flow to the horn.

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"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

Thanks Oldejack - I'm following you for the most part, but still stumped as to the next step. I am using the old horn switch wires and don't see any other candidates. I will try tracing the wires further - especially the disappearing ground one. I guess I'm leaning toward a new separate relay and ditching the built in one. I would really like to put in several more relays for headlights and fuel pump also. Do you think I'm missing something simple or was this circuit most likely flawed from the get go?

Nice Horns by the way! I think pre-electric may have been Lucas' best!

Here's the classic schematic.



This one shows the standard Bosch terminal ID numbers

_________________
"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

Thanks for the diagrams - but your second one is confusing me. It looks in the diagram like terminal 86 is just a switched wire to ground. Shouldn't it be a switched "hot" trigger wire? Also, what do you think is the best source to power the horn button for an all new relay? Off the ignition switch? If so, it it the "S" or the "I"?

Terminal 85 needs to be powered(+) for the horn to work. It is the hot side of the relay coil activation, 86 is the grounding side of the relay coil.

John(Mongo)

Whooops missed that one.
85 and 30 can be jumpered together for a horn, here's a better picture of the Bosch that Painless likes to use.

Actually almost everybody uses some version of this relay.

_________________
"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

Aha! Thank you both - the jumper wire for one power source makes sense as well!