there would not be a ground wire in the steering column for the horns, just the 12V positive. The horn switch just opens or closes the 12V wire that goes to the horns. The ground (negative) side of the battery connects to the frame of the car, making the entire frame of the car the ground. Any device on your car that only has a positive wire going to it is going to get its ground through its connection to the frame. You can use a bolt and nut to attach a wire to the horn where the mounting screw goes. Attach a positive wire to the terminal on the horn. Connect the other end of the wire that is bolted to the horn to the ground post on the battery. Touch the positive wire from the horn to the positive post on the battery. The horn should sound if it is good. if it doesn't work when directly connected to the battery, then there is something wrong with the horn. If you connect the positive lead that normally connects to the horn to the positive lead of your volt meter and connect the negative lead of your meter to the frame of the car or negative post of the battery and press the horn switch, you should see the volt meter move from 0 volts to 12 volts. When you release the switch, the meter should drop back to 0 volts. If you get 12 volts then that means your switch and wiring to the horn are in tact and your problem is most likely with the horn or its ability to get a good ground connection to the battery through its connection to the frame. If the horns test good and you have 12V at the positive terminal of the horn when the horn switch is pressed, try running a wire from mounting bolt of the horn to the battery ground post and retest. Sometimes these ground connections have to run through several bolt on brackets, body to frame connections etc... If the metal between these joints has been painted or corroded, then the parts become insulated from each other and current can't flow between them. You either have to disassemble and clean these contact points or add ground jumpers to bridge the joints. Sometimes it's just a matter of removing a screw that holds a bracket to the frame or body panel and cleaning the screw and the surfaces it contacts to get good metal to metal contact and the screw acts as the ground connection. I hope you find this helpful.