I am trying to replace the horn switch the new switch is 10 amps but the relay that will operate off the switch requires 15 amps and the switch requires a 12 v input, ground connections and positive and negitive connections for the horn how should I wire it
You have some confusion about electrical theory. The relay does not REQUIRE 15 amps. That means the contacts can handle up to 15 amps without overheating. Switches do not require voltage, (electrical pressure). They are typically rated something like "10 amps at 12 volts". That means its contacts can handle 10 amps when it is turned on, and when it turns off, it can handle the resulting arc created by a 12 volt circuit. I'm not doing a good job of describing that, but the switch has to handle the very tiny current the relay needs to turn on.
We use relays because they use a very small current to switch a large current on and off. Without a relay you would need a giant switch. In a horn circuit a 10 amp switch is serious overkill. A one amp or two amp switch would be more than enough. A pair of horns usually draw about ten amps or less so you wouldn't even need a relay if you used a 10 amp switch.
As far as how to wire it, you can look in any service manual for an older car. Newer ones from the mid '90s involve a complicated and unreliable computer. Almost all older cars used a three-terminal horn relay. All relays have at least four terminals. In the horn relays two functions were done by one terminal. If you have the common four-terminal relay, two terminals can be tied together. If you have the equally common five-terminal relay, one is not used.
May, 30, 2013 AT 10:51 PM
So what guage wire should I use?
May, 30, 2013 AT 11:05 PM
14 gauge wire will handle 10 - 15 amps to the horns. 12 gauge will give a little more safety margin. 22 gauge is good enough to connect the switch to the relay's coil. Larger diameter wire, like 18 - 14 gauge is easier to work with though.
May, 30, 2013 AT 11:13 PM
I was just going to hook up the 10 amp switch to the horn my horn is a blazer antique oogah car horn I am not Sure if it is less than ten amps because I would like to not use a relay so use the same guage as you said before or what and I was going to connect the battery right to the switch should I use a fuse and what size
May, 30, 2013 AT 11:57 PM
I don't know how much current those horns draw but I'd be willing to bet it's less than ten amps. You should be okay with 12 gauge wire and a 20 amp fuse. If that fuse blows when there's no apparent problem it could be due to the fact that horn uses a motor. Motors draw higher current to get started, then it drops down in a few fractions of a second. If a 20 amp fuse blows intermittently, switch to a 30 amp but then you should use 10 gauge wire. That's only because the wire should be able to handle more current than the fuse is rated for so the fuse is the "weak link in the chain", not the wire.