Can anyone help with this horn wiring question?

Voltage can read equal to full Battery voltage on a meter, but when a load (horn) is put on it, there may not be enough good wire to allow enough juice to flow through to power the horn.

For example, let's say a wire has 10 tiny strands in it. If just one of those strands is good, it will show full battery voltage on a meter. Depending on the load you place at the end of the wire, though, 1 tiny strand won't be enough to fully power the load. It all depends on how many amps the load draws.

Now, that being said, have you tried removing the leads from the switch and connecting a battery there? If you get a good sound like that, the switch (or wiring leading up to the switch) is the problem. Take a look at the connections at the switch, too - look for that lovely green corrosion to be wicking it's way up inside the wire's sheathing. Might even have broken strands at the switch's connections.

While certainly not impossible, the last thing to suspect is bad wiring between the switch and the horn. But, you'll know if that is the case when you apply a battery directly to the wires off the switch. If the battery makes the horn sound when connected directly to the battery, but not when connected to the wires back at the switch, then the wiring in between is bad.

Unfortunately, these are the type of things you run into with older boats. But, all in all, it's not that hard to fix.
 
I'll respond here rather than THT; you should follow the troubleshooting steps that Ron outlined over there.

Unless it's an intermittent problem with the horn itself- that only happens when you have it wired to the boat's electrical system (not at all likely), the fact that the horn works when connected directly to a battery means the problem lies within the boat's wiring, along the lines of what Ron discussed. A DVM is, as he said, the most useful- and used- tool on my boat.
 
Thats a good idea,I'll try to remove the switch wires and touch those right to a battery. Chances are it is the wiring and not the switch,I seen corrosion on the 2 wires on top of the boat. I try to cut down and clean,but there isnt much wire left,and it is under carpet on the ceiling so I dont know how I would run new wire without ripping carpet,and I really dont want to do that.
I guess we'll see what tomorrows tests bring us.
 
See what happens tomorrow, but if you have to run new wiring there is usually an easier way... Going behind cabinets, cushions, V-berth backrests, etc. Then just make a new hole (as high as possible) in the anchor locker bulkhead and fill with silicone.
 
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