You are right about the steering shaft being part of the ground circuit for the horn. The ground goes down the steering shaft, accross the flexible coupling and finally gets to ground through the steering box. If you look at the flexible coupling you will notice that it is bolted to the steering box 90 degrees from the end of the steering shaft. There is an internal connection in the coupler that transfers ground from one side of the coupler to the other. This connection can get isolated due to corrosion. Same thing happened to me. I went to the local Autozone and got a coupler rebuild kit from the 'HELP' kit aisle and rebuilt the coupler. Cost about $6.00. I've answered this before so I am enclosing my previous response. Sorry for the length.
The way the horn works is as follows:
1. 12volts is always applied to the horn relay.
2. The ground wire from the horn relay goes through the firewall fuse box connector, combines with the turn signal wires and goes up the steering column to the turn signal switch. There it attaches to a spring loaded contact that is attached to the turn signal switch that rides against the bottom of the removable plastic turn signal cancelling cam. The cancelling cam has a contact ring on the bottom. On the top of the cancelling cam there is an extended spring loaded contact that goes through the hole in the steering wheel and contacts the belleville type washer that is between the steering wheel and the horn ring. Note: the contact ring can be cleaned with a pencil eraser.
3. When you press the horn ring, it connects the ground wire from the horn relay (through all of the parts in steps 1-3) to the metal hub of the steering wheel.
4. The hub of the steering wheel is attached to the steering shaft, to the steering coupler, to the steering gear box, to the frame, and ground is applied to the horn relay and your horn blows.
5. The key here is the steering coupler. It is two metal pieces attached at a 90 degree angle to each other to a flexible piece. There is a wire or metal strap that goes from the stud on one metal piece to a stud on the other metal piece. If the wire in the steering coupler is broken or corroded (mine was corroded under one of the studs) the horn will not work or will not work all of the time. You can check this with a volt-ohm meter. Turn the wheel until the horn will not sound and check for continuity across the steering coupler. This should be less than 2-3 ohms. 10 ohms is probably too much to activate the horn relay. The steering column itself is grounded to the dash but the important part is the grounding of the steering shaft. The shaft is not always grounded to the column and probably shouldn't be if everything is assembled properly. Sounds kind of complicated but this is the way the General designed it.
Bob Murray 66 Malibu
Greenfield, Indiana (Indianapolis)
My Artesian Turquoise 66 Malibu
TC Gold #49
[This message has been edited by Bob M (edited 07-10-2001).]