48 Merc horn contact

[laryh]

I am restoring the horns on my 48 Merc. The horns are the ones in the shape of "ram horns". There is a point style contact inside the horns. Can anyone tell me if the contact is normally closed or normally open? And what is the gap supposed to be when the contact is open? Thanks for any info or guesses you can give me.

[rotorwrench]

The Sparton and other FoMoCo horns all work with the vibrator principle. The coil is inergised and vibrates the diaphragm by opening & closing those contacts really fast. In slo-mo the coil pulls the core to a point that the points open which momentarily relax the core and close the contacts whereby the process repeats itself many times a second. The contacts can be cleaned and some minor adjustments can be made for wear by tweeking them a bit. The diaphragm may also have an adjustment for its movement allowance.

Since the construction of these units vary from manufacturer to manufacturer and year to year, I don't know if there was ever enough information published to cover them all. There are a few threads on this board about horns & horn repairs. You might try a search on the subject and see what comes up..

[TomO]

The points should be closed when the horn is not energized. The open gap is not critical and is determined by the armature gap.

On the trumpet horns, I set the gap between the operating arm and the movable contact to .005 and the armature gap between .040 - .050. I don't know the best setting for the sea shell horns.

If one of your horns is working, use that as a guide.

Make sure that you test the horns wit wire that is heavy enough to carry the the current. The jumpers should be at least 12 ga wire.

[laryh]

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Thanks guys! I sort of thought that the horns worked that way but was not sure. Thanks again your answers were a big help.