Polarity for Horn wires

I'm going to splice into the wiring for the OEM horn to add a relay that will enable to use the factory horn button to blow an air horn I installed. There are two wires going into the horn harness which I assume is (+) and ground. I don't have access to a voltmeter right now so was hoping someone could help me with the polarity of the wires. Is the Red wire (+) and the black wire ground as logic would dictate. I don't want to make any bad assumptions and only want to cut the (+) wire for the relay.


I'm wiring the relays as follows to allow the factory horn to be active when upfitter switch is off and air horn to be active when upfitter switch is not on. Please let me know if something doesn't look correct.

Pin 30 - (+) wire from OEM horn button
Pin 80 = (+) wire from upfitter switch
Pin 85 = ground
Pin 87 = (+) wire to air horn solenoid
Pin 87a = (+) wire to factory horn

Moved to Electronics forum as this is not a How-To article.

Bump?


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Yellow with the red tracer is the positive. Now you need to follow up and let us know if the relay works as you described in your op.

it will work if its wired right, I made one for Gedney on the panel I made for him, I made it so one switch turned on the Air compressor and triggered the relay. You have a few seconds of no horn as the air pressure builds up. Then when you fire the steering wheel trigger it fires just the air horn. I'll see if I can find my diagram.

I built a break out harness to do this to mine, I did a write up on it with part numbers for the connectors.
http://www.fordraptorforum.com/f11/need-oem-horn-harness-41049/

Ironhorse07 said:

I built a break out harness to do this to mine, I did a write up on it with part numbers for the connectors.

http://www.fordraptorforum.com/f11/need-oem-horn-harness-41049/

Click to expand...

That link is where you got Jimbo's harness.

So your OEM horn still works and triggers the air horns?


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AbnMP13 said:

That link is where you got Jimbo's harness.

So your OEM horn still works and triggers the air horns?


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Click to expand...

The update In the first post gives the motorcraft part numbers for each side right where the harness plugs into the horns. I think they ran me about $20 from Ford. they are sealed connectors and I have not had any problems. I think it worked out better than cutting up the harness and you have to go in downstream of the OEM horn relay.

The wiring in the OP works perfectly for me. I actually wired the compressor and air horn to the up fitter so that both are hot when the switch is on.

Finally got back and can get a pic, this is how my harness turned out. The ground is tied together in the wire loom and the two hots were extended back to a switching relay. I used upfitter #1 for the compressor and also came off with a 5 amp to latch the relay. So when you turn on upfitter 1 the compressor is powered and the OEM horn button is switched to the train horn.