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Anatomy of a 400/4 Horn (also CB250/360 G5)

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AshimotoK0:

--- Quote from: McCabe-Thiele (Ted) on October 20, 2023, 12:36:23 AM ---Interesting process Ash especially the coil connecting- nothing like as complicated but I have revived old car horns for a short period by connecting one side to the negative side of a fully charged 12 v battery then rapidly connecting & disconnecting the live terminal so it progresses from a dull click to eventually making the horn sound. Only seemed to work for a short period on a seldom used car horn. I thought it was due to the back EMF somehow reviving the contacts.

--- End quote ---

Different problem Ted. On these Mitsuba horns, when not used for 30 odd years, they  develop a hard, totally non-conductive, oxide layer and in this case will not pass any current at all at 12v. You need a very high voltage to discharge through the oxide layer to 'puncture' it repeatedly. If you look back at the beginning of this post, there are other methods but this is my 'go-to' method in the future. Wonder if it will work with open circuit oil pressure and hydraulic brake switches?

Rozabikes Tim:
You are a wizard Ash.

AshimotoK0:
Update on this.

I found a couple of Honda CB400F style Genuine horns in my stash  the other day that were totally dead. My rig to inject EHT to arc across the contacts in order to revive them....  as described on here previously ...  was at work. So I tried removing the M4 adjuster screw/lock-nut completely and with 12v connected across the terminals I repeatedly pushed down inside the hole with a thin crosshead screwdriver to physically move the contacts apart and together again. After quite a few makes and breaks there was eventually a bit of a squeak and the horn started to conduct current, so I carried on making and breaking the contacts and the current gradually increased until the horn worked perfectly, after adjusting the large centre screw and the M4 'tuning' screw. Worked on both horns eventually and worth a try if you have dead horns.

AshimotoK0:
Managed to zinc plate my 400F horn without de-crimping ( pressurised it first and immersed under water whilst still under pressure in order to check it was totally sealed.......which it was and so were the other two horns I had.

This horn was a rusting hulk before I restored it and completely dead electrically (see above). Quite pleased with it now and genuine decent ones are £££'s now, if you can find one....so I guess it was well worth the effort.

taysidedragon:
Better than new! 👍

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