Is the Horn Relay really needed?

[mgeez]

Is the Horn Relay really needed? I see the term "horn relay" everywhere in automotive forums. I am completely rewiring my 51 3600 to 12 volt. I made my own eaier to see and understandable diagram from following the original wiring diagram and it shows no horn relay, nor did I find anything that resembles a horn relay when I cut out all the wiring. Do I need one?
So everyone can critique my wiring diagram, I attached it as a picture, but it is originally created on powerpoint.

[Wrenchbender Ret]

The AD trucks didn't use a relay, but if you are running 12 volts you should put one in the circuit. If you use a horn with only 1 term. You will have to use a relay.

[G&R's57GMC]

On the 6v system (2 wires on horn )the horn was grounded at the steering wheel when the horn button was pushed. Making a large spark that could be seen at night, a bit disconcerting to the driver and passenger. Since most of the trucks saw daytime use it wasn't much of an issue.

On the 12v system the horn (1 wire on the horn) is grounded at its mount. It used a relay that put 12v to the horn when the horn button was pushed and grounded the relay, plus no spark at the steering wheel.

There are 2 wire 12v horns on the market that could be used without a relay but they sound like a foreign car.

[mr48chev]

relays are used to cut the electrical load on the switch that in this case is the horn button along with allowing you to run a smaller size wire to the horn button.

As G&R's57GMC said above some older systems ran a hot wire to the horn button and a wire from the horn button to the horn. Now most electrical systems have a single wire running from the horn relay to the horn button which goes to ground, there is a hot wire that runs from a terminal that usually has power all the time to the relay and then the wire from the relay to the horn. When you hit the horn button you ground that side and it activates the relay which in turn sends power to the horn. That's a bit long and drawn out but on a horn system it usually always works that way.

On other systems with relays you use the relay so that you can get full power to the item you are operating like a pair of high wattage halogen headlights but you don't have the high amp draw through the headlight switch and the dimmer switch or what ever switch you are using for the system you are running.

Hope I haven't added to the confusion.

[OrrieG]

RElays are your friend for any power hog device light lights, radiator fans, most ac components, etc. Read this (whole site has good info on wiring and other stuff) http://www.alanhorvath.com/54chevy/u...ing_relays.php

[mgeez]

Will my orig 6v horn work on 12v? If I understand this right, the only thing the relay will do is minimize the spark at the steering wheel button. If I use a relay, should I place it on the neg side of the horn to complete the ground when the button is pushed?

[skymangs]

OrrieG... x2 on relays are your friend. I relay all my hi-amperage accessories on every build!

[Highsider]

Originally Posted by G&R's57GMC

Making a large spark that could be seen at night, a bit disconcerting to the driver and passenger. Since most of the trucks saw daytime use it wasn't much of an issue.

There are 2 wire 12v horns on the market that could be used without a relay but they sound like a foreign car.

The horn button spark is really funny, and primitive. I never knew this. Thanks!

[mgeez]

Thanks all for the advice. The alanhorvath site really helped me understand.I edited my wiring diagram to include a horn relay.

[G&R's57GMC]

Originally Posted by mgeez

Will my orig 6v horn work on 12v? If I understand this right, the only thing the relay will do is minimize the spark at the steering wheel button. If I use a relay, should I place it on the neg side of the horn to complete the ground when the button is pushed?

No ! The horn button grounds the relay coil. The relay coil causes the relay contacts to close , this feeds the horn 12v from the 12v source.

A relay acts as a remote controlled switch.
Power Flow left to right
Bat._Fuseable link__12v Source_14GA.______/ ________ Horn____________Ground
Bat._Fuse_________12v Source_24GA.__relay Coil______Horn Button _____Ground

The horn wire would be 14 gauge to carry the high current the horn needs
The button wire would be 24 gauge, would be very low current for the relay coil.

[_Ogre]

Originally Posted by mgeez

Will my orig 6v horn work on 12v?

probably yes, in short bursts
it may sound like a little girl screaming though

[Trekster]

I have used the original relays and horns on 12 volt conversions on a 50 truck and a 51 truck. The horn will sound different. You definitely want to continue using the relay.

[1project2many]

Some of the old horns have a screw on the side which can be adjusted to alter tone. I've done this after putting a 12V horn a 24V system.