I know this should be simple but can someone explain the horn circuit under the steering wheel. I know the spring loaded brass pin rests on the metal racetrack on the wheel which connects to horn pad but what allows it to complete circuit from there. If I connect a jumper from the brass spring pin to the metal mount on the signal switch (secured with 3 screws) the horn will work. I can't see how the wheel would contact that metal plate to complete circuit. Seems like maybe I'm missing a part? Couldn't find a close up illustration of this circuit in the wheel. Thanks!

 

All the horn switch does is ground the horn relay , through the turn signal switch harness .

 

No 1978/79 F100/350, Bronco and Econoline has a horn relay unless it has factory installed Speed Control.

With Speed Control, the horn relay attaches to the Speed Control amplifier, located adjacent to the steering column inside the cab.

 

Thanks Guys. With confirmation from 440 sixpack last evening I determined the steering shaft is not grounded. The column housing is. After I connected a jumper from the shaft to engine the horn worked. I'd think it should be grounded through the steering box slip joint but its not. Hmmm. Anyone deal with this before? The u-joint on steering shaft has continuity so no problem there.

 

Yeah, that's a common problem. You need to fabricate a jumper wire for the rag joint.
NOTE: I see you have a highboy. Not sure this is applicable.

 

Yea, no rag joint on the 77 high boy but I will do some continuity checks. Maybe if I'm losing the ground from the steering box slip coupler to the shaft maybe I can attach a ground strap between it and the shaft. Other possibility is losing the ground at the u-joint but initial check indicated there is good continuity through the joint.