No Horn Engine Running but plenty of Horn With Engine Off—Ford Trucks
This may sound like the dumbest thing you’ve ever heard of, but if you look at the electrical diagram it makes a little more sense. Think about it—what controls are on the steering wheel? Cruise Control and the Horn. Ok, if you’ve got a really expensive Ford Truck, you might also have remote radio controls. But for the most part, we’re talking horn and cruise. How does the cruise control know how to behave? Well, it provides power to the switches in the steering wheel. Inside each switch is a resistor. When you operate the switch, power flows through the resistor and then goes to ground. The computer watches to see exactly how much the voltage dropped and by determining that, it figures out what command you’ve just issued to the cruise. Guess what? The horn works the same way. When you press the switch, it completes a path to ground. That activates the horn relay.
My guess is that if your horn isn’t working properly, your cruise isn’t either.
What’s the common thread here? Yup, you guessed it, the ground at the cruise control. In this case you’ll find the “ground” wire from the steering wheel coming into the cruise control servo at pin #6. It’s a dark green/orange wire. The servo is mounted on the driver’s side of the engine compartment. The servo itself gets its ground from the black wire at pin #10. So first check to see if you have good ground at pin #10. If you don’t have good ground there, neither the cruise, nor the horn will work. If you do have good ground, then try placing a jumper wire from pin #6 to pin #10. If your horn now works fine, you can conclude that it’s not getting proper ground from the electronics inside the cruise servo.
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© 2007 Rick Muscoplat
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so the horn has nothin to do with the fuses???