My horn doesn't work, among other things. My manual and wiring diagrams show a horn relay, mounted near starter relay. I don't seem to have one. I do have a thick yellow wire from the starter relay to goes into the horn/headlight harness. I have read in the forum that the horn relay is not required on some 70's and 80's without cruise control, but that's not me.
So, is there another location for the horn relay, I can't find one? It would be nice to know if some 19966 f100 didn't have it, that would be one less thing to try and troubleshoot the horns.
Thanks.
Bill

 

On my 65 the horn relay is on driver side mounted to the inside of the radiator support close to the voltage regulator. I imagine the horn relay is important, on my 65, one side of the 3 prong relay goes to the horn(s), another side goes to a junction for pos. side of batt., and the 3rd goes to the horn button located on the turn signal cam in the steering column assembly. Suggest purchase repair kit, don't believe more than $15-$20, if do so suggest purchase couple extra horn brushes, there are 2 horn brushes in the horn circuit.

 

The relay is necessary, due to the amount of current the horns pull. The current would burn out something without it.
There are 3 wires. It works by grounding the relay through the horn ring; that is one of the 3 wires. When the horn ring is depressed, the 12V energize the relay.
When energized, it pulls current from the battery to the horns, which are grounded through the horn body, using the other 2 larger wires.

Hope this helps.

 

On a 64 the horn tone is adjusted by an internal screw, while measuring current draw - spec is 9 to 10 amps!

 

C4AZ-13853-A .. Horn Relay (Motorcraft HB-79) / Obsolete - Available from auto parts stores.

1965/66 F100/250 2WD - 1966 F100 4WD - 1967 F100/750 - 1968/72 F100/350 // 1965/74 Econoline.

1964 Galaxie/Falcon/Fairlane/Thunderbird - 1965 Mustang w/a generator.

 

My truck is a F100 4x4 and I don't know if it is the same as yours, but here is a picture of my horn relay before restoration (on the left), m.

 

See horn relay parts catalog applications in post 5.