i have a 77 f150. there is no wire going to the horn. cant find a loose wire anywhere. haynes manual says the three wires from the horn relay are yellow-to starter relay, blue/greenstripe - to horn button, and yellow/greenstripe - to horn. my yellow goes to starter relay, my blue/greenstripe goes to cab, but my yellow/greenstripe goes to the external voltage regulator mounted under the horn beside the radiator. the wire looks like it was made into the harness plug, i mean it really looks like it is supposed to be there.

i read a forum post that says trucks with cruise control have horn relays and trucks without cruise control don't, the wire goes from the horn switch straight to the horn. if this is correct my truck should not have a horn relay since it doesnt have cruise control. but....the relay is there.

please advise. i am really confused and frustrated

 

The "no relay" was for 78-79 trucks. Yours should have the relay.
The wire that goes to the horn (yellow/green stripe) on my truck is part of the alternator harness. My v. regulator is mounted just below the horn on th passenger side.
That's correct for the wiring, yellow/hot at all times, yellow/blue trace to horn button, yellow/green trace to horn(s).
The way mine is mounted is the horn relay is mounted close to the starter solenoid. There is a plug in the main harness that plugs into the relay. From there the yellow/green wire travel down towards the alternator where it plugs into the alternator harness. It breaks out of the harness by the voltage regulator and plugs into the horn.
BTW, welcome to FTE, lots of good people here.

 

I wanted to post a pic of the regulator wires but apparently new members are not allowed to attach files to posts. Bummer. There is no wire not attached. The yellow/green is part of the plug that goes into the regulator. Can I splice into that wire and run to the horn? My concern is that the wire I am following might not be the horn wire. I don't want to fry the horn, regulator, or anything else. What would be the purpose of the horn signal wire being plugged into the regulator?

 

Something doesn't sound right. Let me see if I can dig up the wiring diagrams and I'll try and figure it out.

 

I posted some pics on Flickr. Here is the link. The top wire on the regulator is the yellow/green stripe. https://www.flickr.com/photos/61818582@N07/

 

All the wiring diagrams I've looked at show the yellow/green trace running directly from the horn to the relay and not going through the regulator. I can't figure out any reason why it would.
What I would do is run an independent wire from the terminal on the relay to the horn, bypassing the factory yellow/green wire.

 

I'll try that. Is there any way to know which post on the relay is which?

 

Here is the terminal that goes to the horn. The terminal to the right goes to the horn switch and the top terminal is 12 volts.