Do I need a relay for my new horn?

[SKos]

2005 Softail Deluxe (FLSTNI). I picked up a Fiamm Freeway Blaster horn. I've read that some horns require a relay to prevent torching the horn switch and lead wires. I have the service manual and looked at the wiring diagram for that circuit, but I'm an accountant, not an electrician. I can't see a relay in the circuit.

So, do I need to add a relay to the circuit or is there already one on the stock wiring?

I don't remember much from junior high shop class, but I set my multimeter to 200 ohms setting and measured across the stock horn (after disconnecting the power leads) and it measured .8 on the scale. The Fiamm Freeway Blaster also measured .8, so doesn't that mean that the Freeway Blaster is not going to draw any more amps than the factory horn???

Heck, I might not even have the multimeter set on the right setting, I don't know, but I couldn't get anything other than 0.00 readings on any of the other resistance settings. I'm sure this is a stupid question for most of you electronics guys, but I would appreciate your help. Thanks in advance!

[shovelmike]

Your factory wiring does not include a relay, the horn you purchased surely draws more amperage than the pipsqueak horn that the factory installed. What you measured with the ohmmeter was the resistance of the windings in the horn, which is no indication of the amperage it will pull. Excess amperage will quickly burn out your switch.
A relay will enable the low amperage switch to actuate a high amperage circuit for the horn.

[Mavaholic]

Resistance and voltage, is what determines current. Ohms Law says I=E/R
So .8Ω at 12V will give you 15 amps. In theory, both horns will draw the same amount of current, if your measurements are correct. You have to realize wire, connections and switches all have resistance, although immeasurable with the every day meter. If you install a relay, You lessen the amount of connections the current travels through, along with usually heavier gauge wire, which is also less resistance. This gives you higher voltage at the horn. A friend of mine has the same aftermarket horn as I do. His is hooked up to stock wiring. I put mine on a relay. You can hear a difference. As far as burning up the stock wire and switches without a relay, I seriously doubt you will ever do that because the circuit is seldom used. Even when you do, its usually only for a few seconds. Heat is what will destroy the switch and wire and there should not be excessive heat build up in a couple of seconds of use.