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Ref. my 75 F-150. Years back someone rewired the horns with blue wire bypassing the relay etc.
A complete wiring diagram would be to complicated to read....especially for me. Would someone
draw me a simple diagram? It has 3 horns. The third one is a short plastic trumpet mounted pointing down
on the left side of the radiator. It's a neat cord.
Can you post a pic of the relay? Just trying to determine if it's a factory relay (which not all trucks had) or an aftermarket relay.
And you're saying that the additional trumpet horn hnks at the same time as your two factory hi-lo horns?
Can you tell whether the trumpet is fully electric, or is perhaps an air horn with it's own little compressor?
It's possible that the original relay died and the PO just bypassed it, but if that's the case and they did not utilize another relay, then we need to see how it was bypassed as the horn button would either need a relay or it's going to be carrying a lot of current through the single contact point.
If it's a non-relay truck, then that additional current will certainly shorten the life of the horn button contacts. Just too much current passing through them.
Your truck may not have a relay. Let me check the wiring diagrams and get back to you.
My '79 did not have a relay either, even though Ford had used relays since the fifties or thereabouts. If the truck had cruise, it had a relay probably to get one less wire running up to the already busy steering column.
Without cruise, they used two wires (basically power-in and power-out) directly to the horns from the button. Not the best design, but it worked well enough for them when new.
If we can figure out what went wrong with yours I recommend installing a relay like Ford should have, to reduce the load on the horn button/switch.
Might still need a pic or three, but basically yours should have constant power coming into the steering wheel then power out when you push the horn button. Somewhere along that circuit there is a short. I'm thinking it's mostly likely the switch itself at this point.
You can pull the horn button off the wheel and see if the horn stops honking when you disconnect the button from the wheel.
Hmm, according to my Hayne's diagram (could be suspect) yours might have a relay no matter what. If so, it's usually on the passenger side, either along the inner fender apron or radiator core support near the radiator.
Maybe if yours has one, it's near the voltage regulator? Shoot a pic or two of the area around the battery both facing front along the radiator area, and the side along the fender.
Oh, and just FOI (for our information) how many fuses does your fuse panel have?
According to many books the '75 was supposed to have the later model panel with additional fuses, but we've seen at least one '75 with the earlier small panel.
Can you post a pic of the relay? Just trying to determine if it's a factory relay (which not all trucks had) or an aftermarket relay.
And you're saying that the additional trumpet horn honks at the same time as your two factory hi-lo horns?
Can you tell whether the trumpet is fully electric, or is perhaps an air horn with it's own little compressor?
It's possible that the original relay died and the PO just bypassed it, but if that's the case and they did not utilize another relay, then we need to see how it was bypassed as the horn button would either need a relay or it's going to be carrying a lot of current through the single contact point.
If it's a non-relay truck, then that additional current will certainly shorten the life of the horn button contacts. Just too much current passing through them.
Is yours equipped with cruise-control, or not?
Paul
Horn relay - Speed (Cruise) Control has nothing to do with it until 1978.
No horn button on these trucks unless it's a 1978/79 w/a 3 spoke "sport" steering wheel. Otherwise 1973/79, the switch is part of the horn pad.
Your truck will have a horn relay that's located on the right side splash pan near the starter solenoid. It will have three wires: one constant hot (yellow w/ black trace), one that goes to the horns (yellow w/ green trace) and one that goes to the horn pad on the steering wheel (blue with yellow trace).
The way these horns work is when you press the horn pad on the steering wheel, it grounds the circuit and closes the relay making the horn blow.
The third horn you have is an aftermarket piece and, without being there to look at it, it's anybody's guess as to how it's wired.
Here's a picture of the relay. This is a '75
And being a three wire, or three terminal, relay, it almost certainly needs to be grounded to the inner fender, which would normally happen via the bolt securing it.
X2 on take the horn pad off the steering wheel and see if the inner whitish/yellow part (wrapped by the black rubber part) is cracked and causing the problem.
Thanks for the reply. What if I said that all of the horn wires were blue. That means the horn relay is
just an ornament on the right inner fender. That's why I may have asked for a horn wiring diagram.
The wires are always hot.....horn's a blowing. The contact under the horn pad seems OK.
It's actually a pretty simple diagram.
Ignoring any wire colors, you'll have one wire going from a constant 12V source to the relay. Another wire goes from the relay to the horn(s). The third wire will go from the relay to the horn switch in the steering wheel.
The relay itself doesn't "need" to be grounded, it grounds through the wiring.
Here is a page from the factory wiring diagrams that shows the horn circuit. This is a '74 but the '75 is the same. The horn relay is located at position C18 on the diagram (upper left hand corner).
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