Yeah, I’ve got to admit I was surprised when you said the Ford had a constant positive. On most cars that I’ve seen they don’t even run two wires anymore, as they’ll use the horn mount against the chassis as the earth. The wire leading to the horn should only be active when the switch is pressed.
Not sure why they did it but the top of the radiator support seems to be cast aluminum and that’s where the factory horns are mounted. That may be why they went back to 2 wires. Have to check it with a magnet.
Alloy wouldn’t matter. It’s a better conductor than steel.
So you got twin wires coming out of your horn? If so, a quick continuity check should sort out which one is earth and which one is active. If you can’t get an earth with the plug disconnected from the horn then they are using the horn itself as the earth against the chassis and the wires going to it will be an active (switched via the horn button and a fused relay).
Yes I know which one is active. Think it’s blue/white from memory. Black one is the ground. They call “ground” “earth” down under?
Well, we all know what we’re talking about right?, but actually neither term is totally accurate. In 'ye early days a lot of cars were actually a mix between positive earth or negative earth, with the latter being adopted globally for DC auto electrics after everyone went mad trying to figure out what’s what. Now if only they manged to do that for which side the steering wheel is on as well!
Ground was just another term used, but wasn’t fit for purpose either as cars weren’t always grounded. If you’re doing any kind of exam in DC electronics you’ll have to probably still state negative or positive rather than active and ground or earth.
Anyhoo… there’s a bit of trivia for ya.
DBO you ARE the Paintshop Master! I’ve spent the last 3 or 4 days using pencil and paper to draw up my wiring diagram in my spare time. Basically came up with what you did but with a few minor differences. I was looking at using switch 3, with the ignition switched pressure switch and some relays to alternate power between the compressors and electric drain valves. Power can ONLY go to one or the other depending on switch position, both won’t have power at the same time. In your diagram if switch 4 is left in the air horn position, and switch 3 is turned on both the compressor and drain valve will be on at the same time fighting each other it looks like.
And yes it seems like the upfitter relays are completely redundant in this situation as I was planning on relays under the hood to connect the upfitters to. Don’t have the lights yet so I’m not sure of tbe amperage requirements. Was looking at those nice PIAA ones but they cost $250.00. That’s money I could spend on horns! I spoke to HB tech support and tbey recommend 35 amp fuses for both the compressors and valves so tbat’s why I planned on the relays driven by the upfitter switches.
What are these drain valves you guys keep talking about? What’s the purpose?
Your air tank needs a drain valve on the bottom so tbat you can drain the tank on a regular basis to get rid of any collected moisture. They can be either manual or electric.
Gotcha, mine is manual. I’ll stick with that. One less electric part to malfunction. Mine is pretty accessible anyways. Plus I gotta get under my truck every month and drain my fuel filter. Diesel.
Now I’m giving myself a headache. The active wire should have the relay spliced in with battery positive going to the second solenoid terminal yes?
Not sure where you’re getting confused.
Solenoid has two wires. For it to engage it needs one 12V and the other going to the negative (earth/ground). Doesn’t matter which way round that is.
Easy steps:
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Find the active when the stock horn bleeps then tap into that and run it to one wire on the solenoid.
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Run the remaining wire from the solenoid to the chassis somewhere. If you’re mounting the relay onto the car with bolts against metal, then just use a small loop and pin it straight under your mounting bolt. I’d do a continuity check on the ground wire just to be sure.
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before connecting air horns, press horn and check for the click.
The first truck I had an air horn in was my '89 F 150.
There is a local place near me that customizes ambulances, police and fire vehicles. I still go there today because they have the best prices on relays and other odds and ends.
I went there years ago looking for an on-off-on toggle switch. The tech there asked what I wanted it for. I told him I wanted to switch between the factory horn and the air horn. He told me what I really needed was a relay. I said “Uh, um, a relay, what’s that?” He proceeded to explain tbe virtues of using relays and how they can protect your electrical system. I still have the diagram he drew me to connect my horns. He had me splice into the wire in the steering column that comes from the horn switch. Ford now uses low voltage wires with relays so that no longer works apparently. The tech had me connect the relay like this:
Terminal 86: toggle switch
Terminal 30: factory horn switch
Terminal 85: ground
Terminal 87A: factory horn relay
Terminal 87: air horn solenoid(negative)
The other side of the air horn solenoid was battery positive
On my current truck with the two horn wires at the horn location I would splice into the active wire with the relay and connect the second solenoid connection to battery positive still or am I now connecting it to ground?
OK… What your friend gave you there was an SPDT relay circuit, basically allowing either the air horns or the stock horn to operate. It’s essentially an electric version of a manual dual pole toggle switch. You can still do this, nothing wrong with the idea, but you just have to know whether the horn line is positive or negative.
With an air horn (which has a blower motor in it) it’s done like that for load management (i.e. so you don’t overload the horn line). With your Shocker install, the horns are set off by a 12V relay on top of the valve body anyway. There is no real electrical load needed to throw and hold the valve open (only 12V), so using the above circuit is only really useful if you want to exclude the stock horn from sounding at the same time.
You can use a much simpler approach if the above ends up being too confusing.
The toggle switch would be optional (but advisable). It’s not for honking the horn, just to isolate them from blowing when you press your horn button.
The second diagram is how I was going to try it. I’ll get my multi meter out and see what I find.
So was my old horn negative switched and the new one positive? I never checked the old truck I just made the connections the way I was told. If I connect a test lead from my meter to the blue/white and the other to ground and press my horn button, the meter reads 12 volts. If I do the same to the black wire it doesn’t show any voltage.
Any advice on multi meter testing? I own a multi meter but not sure on what settings I should use to test.
Post a pic of your meter. I’ll let you know how you can use it for your install.
Your old car could well have been negative switched but also because you used a steering wheel trigger wire (not the horn relay wire) that is not as unusual as it sounds. Negative switched from the relay would be far less common; in fact I’ve never seen it done.
Anyway, the blue/white in your new car sounds like it is the 12V+ wire which runs from the factory horn relay to the horn. If you want to use the simple circuit idea from my previous post, then use the left pic (positive switched; with the red wire in the diagram being your blue/white )
I used a multimeter under the hood and unplugged the harness that goes into the factory horn. There is a black with purple tracer wire and a blue with white tracer wire. When I plugged the negative probe into the black and the positive probe into the blue I got nothing. When I had someone press the horn inside the truck I got 12.5v at the harness with the way I tested it.
Also ran the positive probe onto the battery terminal and the black probe to the black/purple wire in the harness and got 12.5v.
