Horn Circuit.

[bigmac]

Would anyone know what this circuit would draw?

Thanks,

Fred

[Bitsyncmaster]

A horn is just an electromagnet that makes and breaks the connection via point (like a relay) inside. So your current with be a peak power on and off at the audio rate. You can calculate that peak current by reading the resistance of the horn and dividing that value into 14 volts. Now do the same for the other horn and add both together to get your peak current.

My guess would be about 10 amps.

[Bitsyncmaster]

You got me thinking so I measured the resistance. I pulled fuse #6 and measured the load side to ground while pressing the horn button. I had to do it a few times to get the lowest resistance value. The horn button in my car probably caused a little value change each time. This is always a problem trying read very low resistance values.

Was 0.72 ohms which calculates to 19.4 amps peak.

So if the duty cycle on the horns is 50% (remember they are switching on and off at the frequency) that would read an average current of 9.7 amps.

The designers probably should have used a relay to drive the horns.

[DMCMW Dave]

The designers probably should have used a relay to drive the horns.

In that age American cars typically used a horn relay and Euro cars typically didn't.

[bigmac]

Thanks for that Dave,

I didn't expect it to be so high. The horn contacts in the stalk seem really light weight for that load.

[dustybarn]

The designers probably should have used a relay to drive the horns.

That's the truth. On my car, one of the previous owners added a horn relay, mounted to the crush box adjacent to the left horn, supplied with a dedicated 12V line.

[DMCMW Dave]

Funny thing is I've never seen a horn switch fail other than physically breaking.

[Bitsyncmaster]

Funny thing is I've never seen a horn switch fail other than physically breaking.

It probably burns the contacts but since you rarely use the horn, little failure.

[DMCMW Dave]

It probably burns the contacts but since you rarely use the horn, little failure.

Yup - sounds like good electrical engineering. . .

[pk2678]

Hello,

this is what I did to my horn circuit. My horns have only blown when the engine was running. Without the engine (alternator) running, only a short click was heard.

From the horn switch, a purple/black cable, which is very thin, goes to a connector where the front harness begins. So I cut that purple/black cable. The part that comes from the multifunctional switch now goes to a relay. The output of the relay goes with a thicker cable to the connector of the front harness. An additional thick wire, fused with 20A, to supply +12V to the relay, goes from the relay/fuse compartment to this additional relay. Which is now located below the dashboard. The connection to ground required for the relay is taken from the door light switches. Now the horns sound very good.
In the pictures you can see how it now looks below my dashboard. The second relay is the flasher unit. Usually this is located on a separate board along with the wipe/wash controller. But since the socket of the flasher unit has broken, I moved it below my dashboard.

34373

34374

--Peter

[Bitsyncmaster]

If you need to feed power up front, there are two large ground wires which are used for the headlight grounds and run back to the relay compartment. If you replace the headlight grounds to the frame with new wires, those large (I think they are 12 AWG) wires are available to use and easy to connect to power in the relay compartment.

I used one for my front side light flashing circuit. I made a circuit because I use LEDs in the sidelights and directional lights.

[pk2678]

Thank you for the hint. I will keep it in mind if additional power is required in the front.